What Do These 5 Common AC Noises Mean?

Are you hearing abnormal sounds coming from your HVAC equipment? Trying to figure out what the noise might mean? Check out our list below to learn about possible causes. Make sure to call a certified technician for an accurate diagnosis. 

Screeching or Squealing

Continuous screeching or squealing sounds are usually a sign of damage. A screeching/squealing sound could be caused by failing bearings in the compressor, condenser fan, or air handler, a worn fan belt, lack of lubricant, or a general malfunction. If you hear one of these sounds, call a technician to diagnose the issue. Avoid using the AC until the issue is diagnosed and fixed to prevent further damage.


If you hear a buzzing that was never there before, it could be one of these reasons:

  • Compressor malfunction
  • Refrigerant leak that froze the unit
  • Loose parts
  • Filter needs to be changed
  • Fan blades or fan motor is loose
  • Debris is in the unit
  • Blower is deteriorating
  • Condenser coil needs cleaning

Because there are so many possible causes of a buzzing sound, the best course of action is to get an accurate diagnosis from a technician. Many of these issues are simple fixes, but if the cause is more serious, delaying a diagnosis may become expensive.


Clicking sounds are normal when the system is starting up and shutting down. These should not cause worry. If the clicking is constant, however, this is abnormal and a sign of an electrical issue. The clicking could be caused by a deteriorating thermostat or a larger electrical problem. If the clicking is continuous and comes from the furnace, your ignition system could be malfunctioning. Untreated electrical issues are dangerous and should be investigated quickly by a licensed technician.


If a hissing sound is coming from your AC compressor, it’s likely a refrigerant leak or high internal pressure. Both of these issues can cause a major breakdown and should be diagnosed straightaway. Shut down the AC system and call a technician. If the hissing sound is coming from the furnace, it could be a leak in the air duct. This will also require repair by a technician. 


The most common cause of rattling sounds is a loose or broken part. Loose parts are a quick fix, but should still be diagnosed and repaired by a certified technician. If your part is broken, a new one can usually be ordered and replaced. Louder banging sounds can mean that the compressor, blower, or fan is damaged and needs repair or replacement. Don’t delay calling a technician to diagnose and make repairs, whether it seems like a simple fix or large issue.

The main thing to look out for when it comes to AC noises is frequency and abnormality. If the sound is continuous and frequent, it should be checked out by a technician soon. Many ACs and heating equipment make noise when starting up and shutting down. If you hear new noises that have never occurred before, this may be a sign of an issue. If you are hearing a suspicious sound from your commercial HVAC equipment, call Express Refrigeration in Sacramento, CA today to have a technician diagnose and repair your equipment to prevent a breakdown.