5 Unusual Noises Your Air Conditioning Unit Can Make and What Causes Them

When you’re roasting in the afternoon heat, there’s nothing more refreshing than an air conditioned home. And in the height of summer, you depend a lot on your air conditioning system. So, when you hear unusual noises coming from your air conditioner, it can be easy to imagine the worst.

A healthy unit has a consistent, low hum during its regular operation, so a strange noise can easily stand out. However, not every odd sound means your unit is on the verge of giving out. Below, we’ll discuss some of the unhealthy noises an air conditioning unit can make and what can cause them.

1. Rattling

If you hear a steady rattling from your unit, it may have a loose part. First, check that the screws and bolts on the cover plates are properly tightened.

If they aren’t the problem, you may need to check inside the unit. Carefully remove the cover plates to look inside. Listen for any rattling or loose parts to locate the issue, and then turn off the unit completely at the breaker. Tighten any loose parts you can find, and turn on the unit to check for rattling.

If the rattling persists, it could mean there’re are issues with the motor. Motors are complicated, so contact an HVAC specialist to take a look at and repair the motor. Slight rattling may not be much of a problem, but the louder the rattling is, the bigger the problem is.

However, rattling or soft thumps in the unit could also be caused by accumulated debris. While the unit has grilles in place to keep branches and larger debris out, some bits and pieces of foliage or other debris can get into the unit. Simply turn off the unit at the breaker, remove the cover plates, and clear any foreign obstructions in the unit.

But if you notice any bent fan blades or other damages caused by branches and other debris, call a
professional to make the appropriate repairs.

2. Hissing or Whistling

If you hear any kind of whistling or hissing around your unit, the ductwork seals may have small cracks or openings. Take a look at the duct leading from the unit into the wall to check for any damage or wear.

First, ensure that any screws, bolts, or connections are tight and snug. Examine any of the caulking, and caulk any areas that need it. If the duct seams have been covered with heat tape, ensure the tape is properly adhering to the seams. Replace any heat tape that won’t stick to the ducts.

Hissing or whistling can also indicate a coolant leak. If you suspect this is the case, call your local professionals to investigate. They may need to solder large openings or cracks in the line, or if the damage is extensive enough, they may need to replace the coils entirely.

3. Loud Thumps and Knocks

If you hear some kind of banging in your unit, you may have a serious problem with the motor or with disconnected parts. Broken parts may have fallen into the blades to cause loud knocks, or the issue could simply be a loose fan blade that thwacks the guard as it rotates.

Either way, if you hear loud thumps in your unit, call an HVAC specialist. A part is most likely damaged, disconnected, or broken, and your unit may require part replacements or extensive repairs.

4. Squealing or Screeching

When your unit makes a noticeable squealing noise when it starts up or shuts down, you could be looking at a worn belt or dirty fan rotor. Try cleaning the interior of your AC unit, but if that doesn’t work, contact a local specialist for help.

Like the belt in our vehicles, the AC unit belt can get worn over time, resulting in screeching. If the belt wears down too much, it can break and your unit will essentially stop working. So, while a belt replacement can be expensive, it’s necessary for that blast of cool air in your home.

A technician can determine whether or not your belt needs to be replaced so you aren’t left without air conditioning when you least expect it.

5. Clicking

Your unit may click a bit when it turns on or off. This isn’t entirely abnormal. But if you hear repetitive clicking from the unit or control panel, you may have a defective relay. If you don’t have a lot of experience with electrical work, it can be dangerous to make the repairs yourself. Call a professional to keep yourself safe and your unit functional.


Your air conditioning unit keeps hot summer days bearable and comfortable, so to keep it going when you need it, invest in proper maintenance. Call the knowledgeable technicians at Getzschman Heating to take a look at your air conditioning unit. We’ll inspect the unit and ensure there are no outstanding issues.