AC Making Noise: 12 Fixes to Quiet a Noisy Air Conditioner

In the realm of home comfort, air conditioning systems are the unsung heroes, working tirelessly to maintain your desired temperature. However, one aspect of their performance often goes unnoticed until it becomes impossible to ignore: the noise.

From gentle hums to mysterious clunks and rattles, a noisy air conditioner can be concerning.

Modern HVAC units use sound-dampening technology that keeps the sound level between 25 and 55 decibels, depending on the air conditioner type. Simply put, 25 decibels equals a whisper sound, and 55 decibels equals a normal mid-level conversation at home.

In addition, the latest window and mini-split ductless ACs tend to be quieter than the central ducted systems.  

Air conditioner noises, although quite annoying, can help you know that something has gone wrong before it gets to the point where it cannot be fixed or is just too costly, such as repairing a fan motor or a compressor. 

We have compiled an extensive list of all the AC noises you might encounter and what problems they signify.

This will help you troubleshoot and quiet a noisy air conditioner for improved unit lifespan and a peaceful indoor environment.

1. Banging or Rattling Noise From AC

If you hear an air conditioner rattling noise or noise that sounds like aggressive banging, it is likely a condenser issue, but not necessarily. Here are some reasons with possible solutions to fix this scary noise:

Dirt Particles Getting Stuck in Your Condenser

The banging/rattling air conditioner noise might not necessarily be due to a significant problem and can be easily fixed. Sticks, leaves, and other dirt particles sometimes get stuck in the condenser, which can cause this noise.

For example, if shrubs surround your outside unit, the tiny leaves and twigs can get stuck if you forget to clean the condenser for a while.

Solution: Take off the condenser cover to remove the stuck items. If you find it tricky to handle your HVAC unit, consider calling a professional.

Loose Screws

Many rattling noises are also the result of loose screws. The indoor and outdoor units of an air conditioner vibrate when turned on. Over time, this vibration can cause the screws to become loose.

Solution: This issue is simple to fix; you only need to tighten the screws with a screwdriver.

Broken Fan Motor or Compressor

The worst-case scenario will be if your air conditioner makes a banging noise when starting. It could be due to a broken compressor. On the other hand, if your AC is making a loud noise from inside the unit, it could be due to a broken fan motor or an imbalanced motor causing the bangs.

Solution: Replacing a compressor can be quite costly. If your unit has crossed the decade mark, it is best to let your air conditioner go instead of wasting money on repairs. Here is a great guide on the lifespan of air conditioners.

If your HVAC compressor has a lifetime warranty, you can consider going for repairs, as you will only have to pay for the labor cost. An HVAC specialist will be best able to determine the exact cause and then decide if you should opt for repair or replacement.

Note: Do not inspect the fan motor while running; it can cause serious harm.

Related: Signs Your AC Tune-Up is Due: Keep your AC in Top-Notch Condition

2. Screeching & Squealing AC Noises

Is your noisy air conditioner erupting a high-pitched screeching or squealing noise? This can be due to a variety of reasons:

Faulty Fan Motor Bearings

When you turn your AC on and hear a metal-on-metal screeching noise, the fan motor bearings have become faulty or worn out.

Solution: Here’s what you can do about it:

• Lubricate the bearings: Lack of lubrication or dry bearings can sometimes lead to random noises. However, if the bearings are accessible, you can try lubricating them with oil, grease, or any other lubricant.
• Clean the bearings: Dust, dirt, or debris accumulation can hinder the smooth operation of the bearings. Carefully clean the bearings using a soft cloth or compressed air to remove any contaminants. Be gentle and avoid damaging the bearings during this process.
• Replace the bearings: If lubrication and cleaning don’t resolve the issue, it may be necessary to replace the faulty bearings.

Worn Out or Broken Belt

A worn-out or broken fan belt can also cause a squealing noise. This type of noise is most prevalent in ducted/central air conditioners. In older models, a belt connects the motor and the fan, which can wear out over time.

Further, due to high humidity levels, the belt can also contract and expand in the summer, which can cause unpleasant noise.

Solution: When the fan belt has worn out, you must replace it with a new one. You can DIY; however, leaving this in the hands of an HVAC professional is recommended.

High Pressure in Compressor Unit

If you hear a high-pitched squealing noise from your AC, high pressure has developed in your compressor.

Solution: Turn off the AC immediately, as high-pressure build-up can cause an explosion. Contact an HVAC professional as soon as you can.

3. Air Conditioner Making a Pulsating Noise

If your air conditioner is making slow pulsating noises, there might be nothing to worry about. However, if the noise is loud and rhythmic, it signals a problem.

Loose Fan Blade or Coil

It could be coming from a fan blade or coil that has loosened over time, thus making this AC noise. 

Solution: You simply need to tighten the screws, and your AC will be back to normal.

AC Plastic Base Pulsating

If a plastic base supports your AC, the compressor motion can cause the whole unit to pulsate, along with the base.

Solution: To minimize the vibrations, consider replacing the plastic pad with a wooden one. This can be done by firmly clamping the unit down on the pad and supporting it on small rubber blocks.

Refrigerant Lines Getting in Contact With the AC Walls

A refrigerant line touching the wall can lead to vibrations and friction between the lines and the walls, causing a pulsating noise.

Solution: Slightly move the lines away from the wall and add insulation; this can be done by adding rubber or foam material.

4. AC Making a Hissing Sound

Have you ever felt like a snake has gotten cozy inside your air conditioner because you keep hearing loud hissing noises? Here are the possible causes and what you can do about them:

Leaking Refrigerant

One of the reasons for the hissing sound is a refrigerant leak. Leaking refrigerant can be due to damage to the refrigerant line. Over time, with use, the lines can deteriorate, causing leakage.

Solution: You would have to contact a professional to resolve this issue as there is, unfortunately, no DIY solution for this problem.

Compressor Valve Leak

A compressor valve leak can also cause hissing noise. This is because the valves control the pressurization of the refrigerant.

Solution: In this case, you should not wait to contact an HVAC specialist, as this issue can lead to severe damage.  

High Compressor Pressure

If you feel that the hissing noise has transformed into a shrieking noise after some time, it is a compressor issue. High pressure may have built up in your outdoor AC unit.

Solution:

• Check for obstructions or blockages: Inspect the condenser unit, outdoor unit, and the surrounding area for any obstructions that may impede airflow. Ensure there are no objects, debris, or vegetation obstructing the unit’s air intake or exhaust vents. Clear away any obstructions that you find.
• Clean the condenser coils: Dirty or clogged condenser coils can lead to high compressor pressure. Use a soft brush or a specialized coil cleaning solution to clean the coils
• Verify proper airflow: Ensure that the condenser fan operates correctly and produces sufficient airflow. Check for any loose or damaged fan blades and replace them if necessary.
• Call for professional help: If you can’t seem to figure out the probable cause of the compressor pressure and air conditioner noise, contact an HVAC technician immediately. It can be very dangerous if not dealt with promptly.

5. Clicking Sounds from Your HVAC Unit

A clicking sound at the start and end of a cooling cycle is fine. What isn’t normal is a clicking sound that does not go away. Let’s look at the possible causes:

Obstruction in Your AC Fans

If the outdoor unit is making clicking sounds, there is likely an obstruction in its fans, which needs to be removed.

Solution: Simply perform routine maintenance, lift the outdoor unit’s cover, and clean your fans!

Capacitor Losing Its Charge

Another issue can be the capacitor losing its charge over time. If this happens, the capacitor cannot power the compressor, and the clicking noise you hear is the outdoor unit trying to turn on unsuccessfully.

Solution: If the capacitor is damaged or fails the voltage test, it must be replaced. Purchase a new capacitor of the same specifications as the original. If you’re unsure about the correct replacement part, contact a professional.

Fault in Electrical Signals

Faulty electrical signals can cause the switches to turn on and off, producing clicking noises repeatedly.

Solution: If you see small sparks accompanying the noise, immediately shut down the unit and call an HVAC technician. A spark can become dangerous. Do not try to handle this yourself.

Your AC Fan is Loose

Sometimes, the AC fan becomes loose and keeps hitting your outdoor unit’s case, resulting in the clicking AC noise.

Solution: Call the HVAC service, and they will tell you if the fan can be tightened or needs a replacement.

Malfunctioning Thermostat

A malfunctioning thermostat won’t let your unit turn on, and you will hear a loud clicking sound. During the normal working of a thermostat, you hear a soft clicking sound, the sound of a relay switch sending power to the AC. However, if the relay is broken or there’s a wiring issue, the relay will continue to send power (you will hear loud noises) but fail to turn on the unit.

Solution: You cannot solve this issue yourself; contact a professional for repairs.

6. Whistling Sound Coming from the AC

Is your air conditioner making a noise that sounds like a whistle? This noise may not be as bad as the other air conditioner noises, but it definitely suggests that something is wrong. Here are the possible reasons:

AC Duct Has a Leak

The leaky duct of your central AC can make noises that sound like someone’s whistling.

Solution: The solution is to seal the ductwork properly. In addition to the noise, the leaky duct also causes energy loss, which can increase your bills.

Obstruction in AC Air Flow

If an obstruction blocks the airflow in your AC, the high pressure on the blower motor due to lack of air will cause high-pitch whistling noises. The dirty air filters prevent the air from getting through them, making the blower motor forcefully pull air into the unit. The air passing through the cracks will make whistling noises.

Solution: Cleaning the air filters regularly will prevent this issue in the future.  

7. Air Conditioner Making a Humming Noise

An AC motor radiating soft humming sounds is nothing unusual, but it is concerning when it starts getting loud. Your air conditioner may be humming if:

Lubrication Level is Too Low

A motor that needs lubrication will emit a humming sound in the beginning. But if you continue running it without fixing the issue, it will become a loud grinding noise.

Solution: You can lubricate the motor if you have done it before, but if the issue persists, it’s best to let the professionals do their job.

Contactor Failure

The contactor is responsible for controlling the flow of electricity to your air conditioning unit. A contactor is like a bridge that connects your air conditioner to the power supply. When the air conditioner is turned off, the contactor opens up, disabling the power supply. The reverse happens when you turn it on, and the power supply is resumed.

Contactor failure in your AC causes humming noises as the AC gets power but cannot turn on. If you ignore the issue, it may soon turn into a deafening buzzing sound.

Solution:

• Check Wiring Connections: Ensure all wiring connections are secure and properly tightened. Loose or faulty connections can lead to humming sounds and contactor failure.
• Contact a Professional: It’s important to involve a qualified HVAC technician to diagnose and address any contactor-related issues accurately.

Bent Fin Coils

Humming noises may also come from the fin coils if they get bent.

Solution: You can fix this issue using a metal comb to straighten the bent coil fins. Regular HVAC maintenance keeps your fin coils in the best shape.

8. Cracking Sound Coming From AC

When the temperature is set too low, the moisture is not draining correctly, or the fins are dirty, the coils in your HVAC unit’s evaporator can freeze. Ice falling from these coils makes a cracking sound that echoes through your system.

Solution: To troubleshoot it, disassemble your AC and gain access to the fins. Wash the fins with dish soap thoroughly and let them dry. Only disassemble the AC if you have done it before successfully; otherwise, consider calling a technician.

9. Buzzing Air Conditioner Noise

Is your air conditioner making buzzing noises when starting? This can signify various problems:

Compressor Malfunctioning

If you hear an AC compressor making a noise, it has likely malfunctioned. However, if it is still getting power after it has stopped functioning – a buzzing sound is the result.

Solution: You will need to replace the compressor, which is pricey yet necessary.

Loose Parts

If there are loose parts in your HVAC system, they can cause vibrations while running, which can feel like buzzing sounds.

Solution: Here’s what you can do:

• Visual Inspection: Carefully inspect the AC unit for any visible signs of loose parts. Check the fan blades, motor mounts, panels, and any other air conditioner components that could be causing the buzzing sound. If you notice any loose or damaged parts, it’s best to call a professional for further assessment and repair.
• Tighten Loose Parts: If you feel comfortable doing so and have the necessary tools, you can attempt to tighten any visibly loose parts yourself.

Capacitor Breakdown

A capacitor functions like a large battery in your outdoor AC unit, aiding in the startup of your system. However, over time, the capacitor can deteriorate, leading to a buzzing noise that is only audible near the outdoor unit. Additionally, a failing capacitor might produce clicking sounds, indicating that your AC is struggling to start up.

Solution:  An AC technician will tell you if it needs to be repaired or replaced upon inspection.

Faulty Motor

A faulty motor can also cause buzzing. Moreover, obstructions near the copper lines connected to your AC or the copper lines rubbing against each other can make a buzzing noise.

Solution:  Keeping the lines well-insulated and keeping metal-on-metal contact to a minimum is best to avoid this issue.

Contactor Failure

Your AC’s contactor is responsible for controlling the flow of electricity to the compressor. It can prevent the power from flowing if it malfunctions or wears down. When the HVAC unit tries to start up but cannot because of the defective contactor, your air conditioner will make loud buzzing noises.

As discussed above, this sound will start as a hum, but if left untreated, it can switch to a loud buzz.

Loose Wires

If you hear a steady buzzing AC noise, it is likely due to loosening exposed wires.

Solution: Turn off the AC immediately, as there is a high chance of an electric spark, and have the wiring fixed.

Freezing of AC Parts

If your indoor AC unit is buzzing, it can be due to the freezing of its parts.  Many reasons can cause the indoor unit to freeze, such as the thermostat set too low, low refrigerant, etc.

Solution: To determine which of these problems you are facing, consult an HVAC technician. Read this article for more on air conditioner freezing up.

10. Grinding Noise Coming From AC Unit

A grinding noise coming from your AC can be due to a compressor or motor issue.

Compressor Breakdown

A grinding sound from the outside unit signals a compressor issue. The pistons from a defective compressor produce a heavy grinding noise while operating.

Solution: Replacing the entire compressor is generally recommended rather than repairing its internal parts.

Motor Failure

If you hear grinding noises from the inside unit, your HVAC’s motor failure might be the reason.

Solution: You can prevent this noise by oiling the motor at the beginning of the summer and winter seasons.

11. Bubbling & Gurgling AC Noise

Bubbling and gurgling sounds can easily be confused and could mean the same issue. Here is why they may be occurring:

Improper Sealing of Refrigerant Lines

These sounds usually signal a refrigerant problem. When the air gets trapped in the refrigerant lines, a gurgling sound results. A refrigerant leak can also produce a bubbling noise in addition to a hissing noise.

Solution: The solution is to seal the lines adequately.  

Excess Moisture in Your AC

The excess moisture in the AC can lead to bubbling sounds. A blockage in the condensate drain line creates moisture build-up. This line is responsible for removing the moisture AC collects from your home. As water is unable to exit the line, it makes a bubbling and gurgling noise.

You can face the same issue when the condensate pump gets damaged. It pumps water from the drain pan to the condensate line from where it exits your house. Too much moisture in the pump can lead to bubbling sounds.

Solution: You can disassemble your air conditioner to inspect the drainage line. But it is not advised to change the drain line yourself. Instead, call a certified technician for inspection and repairs.

12. Dripping Sound From Your AC

An AC making a noise that sounds like something is dripping can be a cause of concern. Do not start panicking at once; it might be due to excess moisture falling into the drip pan. This is entirely normal. But it might become a matter of concern when the dripping sound is caused by excess condensation.

High Level of Condensation

A high amount of condensation can cause the drip pan to overflow.

Solution: To remove this noise, you must empty the drip pan.

AC Coils Freezing

When the ice from the frozen coil melts, you will also hear a dripping noise. The coils might freeze for many reasons, including dirty air filters and malfunctioning thermostats.

 Solution: This issue needs to be inspected by a professional.

Why You Should Not Neglect AC Noises?

When your air conditioner is acting out of the ordinary, such as making noise or erupting a smell, it is trying to signal a problem that requires your attention. Neglecting unusual sounds from your HVAC unit can turn minor issues into something detrimental to your system’s health in the long run.

Noise issues can also be dangerous; for instance, a refrigerant leak, signified by a bubbling sound, can lead to refrigerant poisoning in humans. Moreover, ignoring the noise issue can also result in costly expenses, which can be avoided. The sooner you can pinpoint the cause of the noise and resolve the problem, the better it is for your unit’s overall performance.

Taking care of your air conditioner through proper maintenance and regular professional inspections can help prevent strange air conditioner noises. But even then, if you face such an issue, it’s best to find the cause as soon as possible. By solving such problems in a timely fashion, you can prevent expensive repairs further down the road.