Your home's AC should be relatively silent. There may be a gentle hum while it is running or a small click as it powers on or off, but otherwise there should be no jarring noises from the unit. The following guide can help you figure out the problem if your unit is making odd noises during operation, which in turn can help you repair the problem before the AC breaks down.
Rattling noises are most often caused by a loose part inside the air conditioner. It could be as simple as a loose screw on the housing that requires tightening. Another common cause is debris caught in the outdoor AC unit. Small twigs can get inside the housing and lead to vibration noises. Simply remove the cover from the outside unit and clean out the interior with a shop vacuum.
If the rattling seems to come from inside the walls while the AC is running, you may have loose ducts. Your AC technician can trace the noise to the source and better secure the ducts so they no longer make noise.
Squeals, squeaks, and high pitched whistles often originate with the blower fan inside the AC unit. The belt is the most common culprit, especially if the sound tends to only occur at startup. As it begins to wear out, awful squeals are often the result. A tech can replace the belt and solve the issue relatively quickly. In some cases, the cause may be the actual fan itself. The bearings may need to be lubricated or even replaced.
Loud whistling squeals that persist the entire time the AC is running, on the other hand, could be the result of a refrigerant leak. If this could be the case, turn off the AC until a technician can locate and repair the leak.
Bangs and clanks usually indicate a compressor problem. Bangs often result from a broken piston rod or crankshaft, but you can be confident that there is likely an issue in the compressor. Your tech will need to take it apart to see if the problem can be repaired or if it is time for a new compressor.
In some instances, the noise may come from the blower. An out of balance fan blade can lead to bangs, or the blower may simply need to be rebalanced.
Contact a residential HVAC service to have your unit inspected and repaired if you hear odd noises. Companies like Dominion Services Heating & Air Refrigeration can help.