Why Is My AC Making a Strange Noise? What Each Sound Means
June 23, 2026
by Aircommand
Your AC has always had its normal hum the reassuring background sound of a summer afternoon. So when a new noise shows up, a bang or a buzz or a screech you’ve never heard before, it’s hard not to worry. You should pay attention: your system is trying to tell you something.
Different sounds point to very different problems some are minor, and a few mean you should shut the system off and call for help right away. Here’s how to read what your AC is telling you, and when it’s time to call Air Command HVAC. Quick safety note up front: any loud banging, or a buzzing paired with a burning smell, means turn the system off and call a professional before running it again.
1
Banging or Clanking
A loud bang or metallic clank usually means a part has come loose or broken inside the unit often something in the compressor, or a loose component knocking against the housing. This isn’t one to “wait and see” on. Running the system with a broken part rattling around can turn a moderate repair into a major one, so the safe move is to shut it off and call for service.
2
Humming (Especially If It Won't Start)
A soft hum can be normal. But a loud hum particularly when the system is humming yet the fan or compressor won’t actually start often signals a failing capacitor, one of the most common warm-weather failures we see. The good news: it’s usually a quick, affordable fix when caught early. Left alone, though, it can burn out the motor it’s supposed to start. If your unit hums but won’t kick on, don’t keep forcing it, call for service.
3
Clicking
Clicking when your system turns on or off is completely normal. Constant clicking is not it can point to a failing thermostat, a defective control, or an electrical relay problem. If the clicking won’t stop, it’s worth a professional look before it leaves you without cooling.
4
Screeching or Squealing
A high-pitched screech or squeal usually comes from a struggling motor or bearing the blower or fan motor wearing out or, on some systems, high internal pressure in the compressor. None of those get better on their own, and the compressor is the most expensive part of your system, so a screech is worth prompt attention.
5
Rattling
Rattling can be as simple as a twig or debris in the outdoor unit, or as serious as loose hardware and a part beginning to fail. Start by making sure the outdoor unit is clear of sticks and leaves but if a rattle continues after that, something inside is coming loose and should be checked.
6
Hissing or Bubbling
A hiss can mean escaping refrigerant (a leak) or air escaping from a duct; a bubbling or gurgling sound can point to a refrigerant issue or a condensate drain problem. Refrigerant must be handled by a licensed, EPA-certified technician it’s never a DIY fix so a hiss or bubble is a call to the pros. (If your system is also running but not cooling, a refrigerant leak may be behind both.)
What You Can Safely Check
| Clear the outdoor unit of sticks, leaves, and debris. |
| Replace the air filter if it’s dirty airflow problems can cause some noises. |
| Note when the sound happens (startup, shutdown, constantly) and what it sounds like it helps us diagnose faster over the phone. |
| For any loud banging, buzzing-with-burning-smell, or grinding, turn the system off and leave it off until it’s inspected. |
If the noise is anything more than a stray twig in the fan, the cause usually lives inside the system’s motor, electrical, or refrigerant components where a trained technician needs to look.
Serving the Whole Wiregrass
From our home base in Hartford, Air Command covers Dothan, Enterprise, Holmes County, and the surrounding communities across southeast Alabama and the nearby Florida panhandle licensed in both states (AL #07115, FL #CAC1821341). Not sure if you’re in our service area? One quick call to (334) 684-1060 and we’ll let you know.