Malfunctioning air conditioning systems can exhibit a number of different noises. Understanding what a few of the most common noises associated with a damaged air conditioner are and what the problems those noises point to are can help you diagnose problems quickly. This can help an HVAC professional repair your system quickly, reducing the chances of additional mechanical problems developing and restoring your system's efficiency as quickly as possible.
A high-pitched whistling sound coming from your vents indicates that part of your ductwork has sprung a leak. This happens normally with age as the seal between sections of your ducts wears down, but can also occur in newer systems that are damaged during home construction or remodeling – or are installed improperly. A leak in your ductwork can cause your energy bills to go up over time, since your air conditioner will be able to supply less air to your home and thus will have to work harder to hit the setting on your thermostat. You'll have to have the offending section repaired or replaced entirely, depending on the size of the leak.
Though banging coming from your air conditioner while it is turned on may seem like a very serious issue, more often than not it is simply a hose or section of ductwork that has had its fastener loosen over time. This means that as your air conditioner moves air throughout its system, that specific component will shake or bang against something else. This doesn't mean that you should simply let it be, as continued banging can lead to damage to y our system that could cause a leak or a more serious mechanical issue to develop. Usually, the matter can be easily resolved by a professional simply tightening the screws or installing an entirely new fastener on the offending section of your system.
A long, high-pitched screeching indicates that the motor within your blower system is burning out, or the fans within your system have somehow become damaged and are rubbing up against another metal surface. This will be distinct from the whistling that comes with an air duct leak, as the sound is much more aggressive and grating as it is mechanical in nature. While rare, a burned out motor or damaged fan will require the entire blower system to be replaced – depending on the age of your system, it may make more financial sense to simply replace your entire unit with a newer, more efficient model.