AC Troubleshooting: What is that noise?

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Why is my AC so loud

Today’s air conditioners are built to be quieter than ever. High-efficiency units incorporate sound-dampening technology and variable speed compressors to keep noise levels low.  So, ignoring odd noises your AC makes can turn minor issues into a major expense. Some of these noises could signal anything from needing a simple tune-up to costly repairs, or even replacement of the entire unit. The sooner you address the cause of the noise and resolve the issues with your system, the better.

Here are a few of the common sounds your HVAC system could make, the most likely cause, and what to do:


Situation: A high-pitched whistling or screaming sound that occurs when the outside unit first turns on. The noise usually lasts 10-15 seconds before stopping and the system may shut off and turn back on frequently.

Most likely cause:  Compressor. There is probably a high internal pressure build-up in the compressor.

What to do: If you hear high-pitched whistling or screaming from your system, shut it off and call a professional immediately. A high-pressure build-up can be dangerous.


Situation: When the outdoor unit is running, there is a clanging or banging noise coming from it.

Most likely cause: The outdoor unit’s fan is hitting something. Some debris (like a stick) may have fallen into the unit or the fan has come loose is hitting its protective cage.

What to do: Turn off your AC and call a professional. If you continue to run your air conditioner, it could cause larger problems.

Clicking (while the unit is running)

Situation: There are repeated clicking noises coming from the outside unit and get faster and closer together as the air conditioner turns on.

Most likely cause: An obstruction in the outdoor unit’s fan.

What to do: Turn off the unit and remove the obstruction, then continue to run your air conditioner. But, if you have doubts about removing an obstruction from the fan, don’t hesitate to call a professional.

Clicking (the unit won’t start)

Situation: Steady clicking noises when the unit is trying to turn on, but doesn’t, and just continues to click.

Most likely cause: There is an electrical problem. It may be a faulty thermostat, compressor issue, or capacitor.

What to do: Call a professional.


Situation: The air conditioner turns on, the outside unit makes a loud metal on metal screeching noise and does not stop until the unit shuts off.

Most likely cause: The fan motor bearings are bad.

What to do: Call a professional. You’ll need to have your fan motor replaced.


Situation: There is a squealing noise coming from inside the unit. It may come and go, but it is usually regular.

Most likely cause: The fan belt is misaligned or worn. Some units have a belt that connects the fan and motor that can become misaligned or worn out over time. The sound can come and go as temperatures and humidity levels cause the belt to expand and contract.

What to do: You can continue to run your AC, but the belt may break leaving you without air conditioning. Call a professional asap to get the belt fixed or replaced.

Metal Popping

Situation: You hear the metal ductwork popping when the system turns on or shuts off.

Most likely cause: Metal contracts and expands with temperature change, so your ductwork may noisily pop open or clang shut.

What to do: This not harmful to your system, but you can use insulation or foam to cut down on excess noise.

If you hear an unfamiliar sound that may indicate there is an issue with your air conditioner, it is a good idea to turn the unit off and schedule a service appointment with us.

While it is never convenient to have a broken AC, a yearly inspection and tune-up can prevent future problems. Burkholder’s HVAC offers maintenance agreements with many benefits including 24-hour emergency service with no overtime rates.