Advanced Air

6 Loud Air Conditioning Noises and Their Causes

July 15, 2015

Is your air conditioner making a loud, annoying noise? Want to know if it’s serious?

Here are the 6 most common noises an air conditioner makes along with their causes.


The situation: A high-pitched hissing or screaming sound. Occurs at the outside air conditioning unit when the AC first turns on. Usually lasts 10-15 seconds before stopping. The AC unit itself may shut off and turn back on frequently.

Most likely cause: Your compressor. There’s probably high pressure building up in your system, causing the compressor to scream.



The situation: When the outdoor unit runs, there’s a clanging or banging noise coming from it. The noise doesn’t happen with you turn your thermostat to FAN.

Most likely cause: The outdoor unit’s fan is hitting something. Could be an obstruction that shouldn’t be there (like a stick) or that the fan has come loose from the mount and is wobbling and hitting its protective cage.

Should I keep running my AC? No. Continuing to run your air conditioner could cause even bigger problems. Turn your AC off and get it fixed by a professional air conditioning contractor.

Bubbling/gurgling noise

The situation: A gurgling noise while your air conditioner runs. It may be difficult to tell exactly where the noise is coming from.

Most likely causes: The condensate drain line is gurgling, or your AC may have a refrigerant leak. 

Should I keep running my AC? It probably won’t hurt anything. Make sure your condensate drain line has a proper trap. If you think it’s a refrigerant issue, have a professional check it out.


The situation: When your air conditioner turns on, the outside unit makes a very loud screeching noise — like metal on metal. The sound persists until the unit shuts off.


Should I keep running my AC? You can continue to run it if you absolutely have to (like in 100-degree heat while you wait for a repairman). But get it fixed ASAP.


The situation: When your AC, heater or fan is on, you notice a squealing noise coming from your inside unit. It may come and go but it’s fairly regular.

Most likely cause: The fan belt is misaligned or worn. Some units have a belt that connects the fan and motor. Over time this belt can wear out or become misaligned, leading to a squealing noise. The sound can come and go as different temperatures and humidity levels cause the belt to expand and contract.

Should I keep running my AC? You can continue to run it, but the belt may eventually break and leave you without air. So get it fixed.

Clicking (while unit is running)

The situation: Repeated clicking noises coming from the outside unit that gradually get faster and closer together as your air conditioner turns on.

Most likely cause: A small obstruction in the outdoor unit’s fan (think of baseball cards in the spokes of a bike wheel.)

Should I keep running my AC? Remove the obstruction first. Then continue to run your air conditioner.

Clicking (unit won’t start)

The situation: Steady clicking noises when your outside air conditioning unit tries to turn on. The unit doesn’t turn on, but continues to click.

Most likely cause: There’s an electrical problem that needs to be corrected. It could be a faulty thermostat, a compressor problem or a capacitor.

Should I keep running my AC? N/A since the unit won’t start.

Is your AC making a strange noise? Want a professional to take a look?

Advanced Air serves Southwest Florida—including Fort Myers, Naples, Cape Coral, Estero, Bonita Springs, Port Charlotte and more. Give us a call or contact us online for help with your air conditioning noise.