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Why Is My Central Air Conditioner Making a Loud Noise? A Minneapolis‑St. Paul Tech Answers

Tired of that loud, obnoxious noise coming from your AC?

We don’t blame you.

Here’s the thing: Loud noises are usually a sign something is (seriously) wrong with your AC. So the first thing you should do is call a professional to diagnose the problem and fix your air conditioner.

But if you’re curious what could be causing that loud sound you’re hearing, we’ll explain the source of 5 loud AC noises:

  1. Banging sound
  2. Buzzing noise
  3. Clicking sound
  4. Hissing noise
  5. Screeching/squealing sound

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Loud noise #1: Banging

Do you hear a loud banging noise coming from your outdoor unit?

If so, it’s probably the compressor. Your AC compressor is the part that’s responsible for circulating refrigerant (the liquid/gas that cools your home’s air).

air conditioner compressor

An air conditioner compressor

Due to normal wear and tear, parts inside the compressor can become loose and create a loud banging sound as they rattle around inside the compressor’s outer casing.

Unfortunately, it’s rare that a tech can repair your compressor in the field. In most cases, you’ll need to get a new one entirely (check to see if it’s covered under your AC manufacturer warranty). You see, the compressor is hermetically sealed, meaning the tech can’t open it without damaging the outer shell, which would render it useless.

For more information about replacing a compressor, read our article, “How Much Does it Cost to Replace an AC Compressor in Minneapolis-St. Paul?”.

Loud noise #2: Buzzing

Buzzing noises can be heard inside (near the air handler) or outside your home (near the outdoor unit). A buzzing noise is typically a sign that you have an electrical problem.

central air conditioning diagram

The outdoor and indoor unit in your AC system

Common electrical AC problems include:

  • Failing motor
  • Loose wiring
  • Broken capacitor
  • Malfunctioning compressor
  • Arcing (when electrical current escapes the intended path, causing sparks)

Loud noise #3: Clicking

A loud clicking sound could be caused by a couple different AC issues. It depends on where and when you hear the clicking noise...

  • If you hear the clicking noise while the AC is running, it could mean a small object has nestled its way into your blower fan, so the object hits against the fan as it spins.
  • If you hear the clicking noise when you try to start your AC (but it won’t start), that’s usually a sign of an electrical issue within the thermostat, compressor or capacitor.

Loud noise #4: Hissing

A hissing noise could be a sign of the following AC problems:

  • Duck leak
  • Bad expansion valve
  • Air filter that doesn’t fit correctly in its slot

… but most likely, the hissing noise is a sign of a refrigerant leak.

During normal operation, refrigerant runs in a closed loop in your AC system. But over time the thin, copper lines and coils that carry the refrigerant can form leaks, allowing the refrigerant to escape.

Since the pressure inside the copper tubing is high, when refrigerant escapes it makes a hissing noise (think of air escaping a balloon).

To learn other signs you may have a refrigerant leak, read our article, “How to Tell if Your Air Conditioner Needs More Refrigerant (Freon).”

Loud noise #5: Screeching/squealing

Loud screeching (like metal grinding on metal) and squealing sounds are generally caused by the following AC issues:

  • A bad compressor
  • Bad outdoor fan motor
  • Faulty blower motor

The cause of the sound depends on where you hear it.

Does the loud screeching/sound come from the outside unit?

Then it’s probably 1 of 2 problems:

  • A bad compressor. If the motor inside the compressor goes bad, it can cause a loud screeching noise.
  • A faulty fan motor. Your outdoor unit has a fan that helps expel heat from refrigerant. An issue with this fan motor can create a loud screeching sound while the AC is running.

Does the loud screeching sound come from indoors?

Then the problem is probably the blower fan motor.

The blower fan is responsible for pulling warm air from your home to be cooled, then pushing that cold air back into your home.

However, over time the bearings in the fan motor can give out (usually making a screeching sound) or the fan belt can wear out, causing a squealing noise.

Need a Minneapolis-St. Paul AC pro to stop the noise?

Just contact us.

We’ll fix whatever is causing your AC to make that loud noise. Visit our heating andcooling page to learn more about the AC services we offer.