8 Common Noises Your AC Makes and What They Might Mean

If you hear unusual sounds coming from your AC unit during normal operation, don’t ignore them! Noises can be a sign that your unit needs a repair or upgrade. By ignoring the noises, a minor issue can turn into a major expense.


Banging is usually a sure sign that there’s a loose or broken part inside the air conditioning compressor. It could also mean the indoor blower is unbalanced. A third possibility is that your system needs a compressor replacement.


Clanking is another sign of a loose or out-of-balance part. The parts inside the sealed unit have likely failed and the compressor itself may have become loose. Clanking can also be a sign of the indoor blower or outdoor fan and its blades are out of balance and hitting other parts.


The clicking of electrical components at start-up and shutdown is a normal part of the system’s operation, but constant or ongoing clicking is not typical. It can be a sign of a defective control or a failing thermostat. There are a lot of electrical parts in your unit, so it’s critical to pay attention to potential electrical issues as soon as possible.


A buzzing noise from your outside unit could mean:

  • Loose parts
  • Debris in the indoor or outdoor unit
  • Outdoor fan motor is loose or about to fail
  • Fan blades are loose or out of balance
  • The copper lines from outside to inside are rubbing against something
  • The condenser coil needs to be cleaned
  • The air filter needs to be changed
  • The blower is going bad or out of balance
  • Refrigerant leaks, resulting in your AC freezing up. If your AC is not cooling, this could be why.


Blower and fan noises such as squeaks, squeals, and rattles may be transmitted through the duct system. Outdoor fan motors and indoor blower motors squeal loudly when they’re going bad. The blower wheel and housing will also squeal when they malfunction. For some units, this sound is normal upon start-up. You should be able to identify whether it’s a sound that the unit always makes or if it’s new.


A humming sound generally isn’t serious, but it still signals that something inside your AC is off. Loose parts and refrigerant piping can cause vibration and if left unchecked can lead to a more serious maintenance issue. Humming or buzzing can also be a sign of an electrical problem. If the compressor hums and refuses to start, there may be an issue with the motor, though loose wiring could also trigger the noise.

Chattering or Rattling

A rattling noise can mean that your AC is starting to deteriorate, and some of its parts are loosening. Another cause could be twigs or leaves that have clogged your system. The electrical contractor in the equipment can also make a chattering sound which can damage other components including the compressor if allowed to continue. Another culprit could be the fan, which rattles when loose. Your first line of defense is to check for loose screws or bolts in the unit’s casing, clean condenser coils, and change your indoor air filter.


If you hear high-pitched whistling or screaming, shut the air conditioner off and call us right away. The most likely cause is a refrigerant leak, which not only damages your air conditioner but can also threaten your family’s health. Screaming might also indicate high internal pressure within your compressor, which is VERY dangerous. If your AC turns off on its own, don’t panic. It’s a good thing—a sensor is doing its job to protect you from a potentially hazardous situation.

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8 Common Noises Your AC Makes and What They Might Mean

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