Why Does My AC Sound Weird?

young woman covering her ears with fingers from air conditioner noises at home

If you suddenly wonder, “Does my AC sound weird?” it probably does. Older air conditioners typically produce light buzzing noises from the indoor and outdoor units, while the newest energy-efficient models produce little to no noise. If a new sound is grabbing your attention, there could be a problem with your AC system. An air conditioner making sounds should not be ignored. You can call an HVAC technician to check out your air conditioning system and repair it if necessary, or you can try to diagnose the problem yourself. Some issues are easy to fix if you are even a little handy. 

Why Is My Air Conditioner Making Sounds?

Some noise coming from your air conditioning unit is not necessarily something to be concerned about, but there are some sounds that your air conditioner should not make. Banging, screeching, humming, buzzing, rattling, clicking, hissing, and bubbling noises could indicate minor to serious problems. 

Banging Noises

Banging noises are usually caused by a broken or damaged part within the compressor banging against the framing. The compressor circulates refrigerant between the indoor and outdoor units to cool the warm air inside your home. Over time, the compressor’s components may get loose or break. Compressor issues are problematic because they usually need to be replaced if they’re damaged. Replacing a compressor also tends to be expensive, so some homeowners opt to replace the entire air conditioning unit. 


Banging noises could also signal a problem with the blower assembly or motor, such as an unbalanced internal blower, loose motor mounts, or loose fan blades on the blower fan or compressor fan.


If you hear banging noises, especially if the banging noises become louder when the blower is running, immediately turn your system off. Disconnected or broken parts can cause further damage by banging into other parts. Call an HVAC professional to inspect your AC unit.

Screeching Sounds

Screeching, screaming, or squealing sounds usually indicate a problem with the indoor blower motor, outdoor fan motor, or compressor. You may be able to pinpoint the problem by noticing when the noise occurs. 


If the noise occurs the entire time the air conditioning runs, the problem is probably the outdoor fan motor or the indoor blower motor. The fan motor may need to be replaced or have a loose belt. The bearings may need to be lubricated if it sounds like metal rubbing against metal. Depending on how handy you are, you may be able to reposition or replace the fan belt and lubricate the bearings. The same noise could also be caused by dry bearings or damaged blower wheels on the indoor blower motor. 


If the noise only occurs for ten to fifteen seconds when the air conditioner first starts up, it is probably the compressor. These sounds could be a dangerous sign that the compressor is over-pressurized or has a refrigerant leak. Immediately turn the AC unit off and do not use it until you have an HVAC technician inspect it. 

Humming Noises

An abnormal humming sound from your air conditioner could be caused by loose parts vibrating, such as the refrigerant piping. It could also be an electrical problem such as loose wiring or a defective relay switch, a device that starts the outdoor condenser unit when it receives a signal from the thermostat. Get potential electrical problems inspected by a technician. If ignored, electrical issues can cause further damage to the unit. 

Buzzing Sounds

Various issues could cause a buzzing sound. Locating where the sound is coming from may help diagnose the problem. 


If the sound comes from the outdoor condenser unit, the problem could be an electrical issue such as a faulty relay switch. As previously mentioned, a relay switch is a device that starts the outdoor condenser unit when it receives a signal from the thermostat to turn on. It could also be related to the fan motor, loose fan blades, or debris inside the unit obstructing the fan. 


Dirty condenser coils or loose parts within the outdoor unit, such as the rubber isolation feet on which the compressor sits, can produce a buzzing sound, too. 


The most severe issue would be a refrigerant leak. A refrigerant leak is likely if the unit seems to be working, but warm air is coming from the vents. It is best to call a technician to inspect electrical issues, fan motors, refrigerant leaks, and issues involving the compressor. 


If the sound comes from the indoor evaporator unit, it could be an electrical problem involving the circuit breaker. If your air conditioner uses more amperage than the breaker can handle, it may make a buzzing noise or trip the breaker. A dirty air filter can also affect the circuit breaker. 


Ice on frozen evaporator coils in the indoor unit is another possible source of a buzzing noise. Evaporator coils can freeze if the unit has a leak caused by damaged refrigerant piping, a faulty expansion valve, or improper installation. Frozen coils can also be caused by something as simple as a dirty air filter, which decreases air circulation. 


You may be able to resolve the problem if the noise is due to frozen evaporator coils and is not the result of a refrigerant leak. 

  1. To thaw the unit, turn the switch on the thermostat to “off.” Keep the unit off until the ice melts. 
  2. Turn the fan switch on the thermostat to “on.” The circulating air will help thaw the coils.
  3. Inspect the air filter and replace it if it is dirty. 
  4. When the ice has melted, turn the switch on the thermostat back to “cool” and the fan switch to “auto.” If the coils still freeze up or the buzzing sound continues, contact an HVAC technician. 

Rattling Noises

Leaves, sticks, dirt, and other debris can clog up your AC system and cause a rattling noise in your outdoor unit. This issue is relatively easy to fix. Shut off the power to the unit, remove the metal cage surrounding the unit, and remove the debris. While disassembling the unit, you can clean the condenser coil by carefully vacuuming it with an attachment, gently rinsing it with the hose, or applying a coil cleaner. Loose parts can also cause a rattling noise, so check screws and bolts to ensure they are tight, and look for other detached parts. For good measure, change the air filter in the indoor unit.


As mentioned, loose parts inside the outdoor unit can make a rattling noise. If you discover any loose parts or suspect they are the problem, have your unit inspected by an HVAC technician. Loose parts being flung around can cause further damage to the unit. 


A loose, unbalanced fan in the indoor or outdoor unit can cause a rattling or clanking noise. Loose fan blades can strike and damage other parts of the unit. An HVAC technician can usually reposition the fan. 


Rattling can be caused by an electrical problem such as a damaged contractor. A technician should inspect this problem before it damages the compressor. Malfunctioning compressors usually have to be replaced, which is expensive. 

Clicking Sounds

It is usually normal to hear one click from the thermostat at the beginning and end of a cooling cycle. If you hear multiple clicks when the AC turns on and off, there is likely an electrical problem like a defective contactor or relay.


Hearing clicks throughout the cooling cycle could indicate problems with a relay switch, the capacitors in the compressor, or a failing thermostat. 


Always get electrical problems inspected by an HVAC technician. Hold off on installing a new thermostat in case it’s not the problem. If the thermostat is the issue, a technician or a licensed contractor can install a new one to ensure it’s installed correctly. 

Hissing Noises

A hissing noise could indicate a refrigerant leak, a significant problem. Air conditioners use refrigerants to remove the heat from the air inside your home. The refrigerant makes a hissing noise when it leaks because it is a gas under pressure. The refrigerant can leak from the copper lines that carry it or a faulty part like the Schrader valve. 


A hissing noise could also be an initial sign of extremely high pressure within the compressor. The hissing sound will later turn into a squealing noise, a more common signal of a dangerously over-pressurized compressor. 


An air duct leak may produce a hissing sound. This issue can be caused by a faulty expansion valve or the wrong air filter for your AC system. Check the air filter to make sure it is compatible.


Turn off your AC system until you get the hissing noise inspected by an HVAC technician. Refrigerant leaks and over-pressurized compressors are serious problems that require professional help. Only licensed technicians can handle refrigerants, so a professional is needed to repair the problem and recharge the system. 

Bubbling Sounds

A bubbling sound could indicate that there is too much moisture being produced by the AC system or a problem with the drainage pipe. A dirty air filter or a refrigerant leak can cause the indoor evaporator coils to freeze. Excess moisture flows into the drainage pan as the ice melts. A bubbling sound may also be produced if there is a blockage, crack, or hole in the drainage pipe. If you are handy, you can inspect the evaporator coils and the drainage line yourself. Please remember to turn off the power to the unit before disassembling it. Do not try replacing the drainage line yourself. Call a professional. 


A bubbling sound may also indicate a large refrigerant leak. Once again, refrigerant leaks are serious and must be repaired and the system recharged by a licensed HVAC technician.

What to Do Next

If your AC makes a weird sound, try to locate where the sound is coming from to diagnose it. You may be able to resolve some issues, like removing debris and changing the air filter, on your own. A licensed technician is needed to handle refrigerant leaks and more extensive repairs. Routine inspections and maintenance of your AC unit can help you avoid problems in the future. 


If you need parts for your AC unit or an entirely new system, we can help. The Furnace Outlet offers the lowest prices on residential HVAC supplies online. Please contact our experienced technicians with any questions or concerns you may have, and we will be happy to help. 


Contact Info
Email: help@thefurnaceoutlet.com
Phone: 888.286.0211

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