Why Is My AC Making a Strange Sound When It’s Running?

How Loud is Too Loud? Decoding Weird AC Noises

Odd noises coming from your air conditioner aren’t just annoying—they’re usually your system’s way of telling you that something’s wrong. Whether it’s a clicking, buzzing, hissing, or banging noise, understanding what these sounds mean can help you take the right steps before a small issue becomes a major (and expensive) repair. Consider this your noisy AC troubleshooting guide!

At Pittsburgh’s Best Plumbing, Heating & Air, we’ve heard it all. If your AC is making a strange sound, here’s what you need to know—and when to call in a professional.

Common AC Sounds and What They Mean

• Banging or Clanking

Loud banging or clanking is usually a sign of a mechanical issue, often with the compressor or fan blades.

Possible Causes:

• Loose or broken parts inside the compressor

• Bent fan blades striking other components

• Unbalanced blower or motor assembly

Fix it fast: This type of sound often indicates something has come loose and is moving around in the system. Continuing to run your AC in this condition can lead to more serious (and costly) damage.

• Buzzing or Humming

A consistent buzzing or humming noise could point to either electrical problems or obstructions in or around your unit.

Possible Causes:

• Loose wiring or a failing motor

• Condenser coil covered in debris

• Malfunctioning contactor relay switch

• Electrical arcing

Don’t DIY this one: Electrical issues are dangerous to handle on your own. Turn off the unit and call a licensed technician.

• Clicking

If you hear clicking when the system starts or stops, that’s fairly normal. But constant clicking while your AC is running could mean something is off.

Possible Causes:

• Faulty thermostat

• Control board issues

• Electrical relay problems

Pro tip: If the clicking is coming from the outdoor unit, it could be a failing capacitor or contactor—both of which require professional diagnosis.

• Hissing or Whistling

A hissing sound could signal anything from an air leak to a refrigerant issue—both of which should be addressed quickly.

Possible Causes:

• Refrigerant leak (especially dangerous and requires licensed handling)

• Leaky ductwork

• Compressor valve leak

• High internal pressure in the compressor

Refrigerant leaks are serious: Not only can they reduce your system’s performance, but refrigerant exposure can be harmful. Call for service immediately.

• Screeching or Squealing

If your AC is screeching like a banshee, that’s often a mechanical issue that’s about to get worse.

Possible Causes:

• Worn-out fan belt

• Failing blower motor

• Bearing issues in the fan motor

Loud = urgent: These sounds usually indicate parts that are worn or rubbing together. Shut off the unit to prevent further damage and call a technician.

• Rattling or Vibrating

Rattling often signals that something is loose inside the system.

Possible Causes:

• Loose panels or screws

• Debris in the outdoor unit

• Failing motor mounts

Check the basics: Sometimes, tightening a panel or clearing out a few leaves can fix the issue. But if the rattling persists, a deeper problem may be at play.

Why You Shouldn’t Ignore Strange AC Noises

It’s tempting to ignore odd sounds—especially if your air conditioner still seems to be cooling your home. But here’s why that’s a mistake:

1. Minor issues can become major repairs

A loose fan blade may start as a rattle, but left unchecked, it can break free and damage the motor.

2. Efficiency takes a hit

When parts aren’t functioning properly, your system works harder, using more energy and raising your utility bills.

3. You risk a full system breakdown

What starts as a squeal could end in a seized motor or compressor failure—two of the most expensive HVAC repairs.

What Should You Do When Your AC Makes a Strange Sound?

The right response depends on the type and severity of the noise. Here’s a general game plan:

Step 1: Turn Off the Unit

If the noise is loud, persistent, or alarming—shut it down. Running it could make the damage worse.

Step 2: Take Note of the Details

• What kind of sound is it?

• When does it happen—startup, shutdown, or continuous?

• Is it coming from the indoor or outdoor unit?

Step 3: Check for Obvious Issues

• Are there leaves or debris in the outdoor unit?

• Are any panels visibly loose?

• Is the thermostat functioning properly?

⚠️ Caution: Never open electrical panels or attempt refrigerant work unless you’re a licensed HVAC professional.

Step 4: Call a Trusted HVAC Technician

The safest move is to let a professional inspect and diagnose the issue. The team at Pittsburgh’s Best is trained to pinpoint the source of strange AC sounds and recommend the most effective (and affordable) fix.

Can Strange AC Noises Be Prevented?

In many cases, yes. Preventative maintenance is the best defense against strange sounds and breakdowns.

Schedule Annual AC Tune-Ups

A professional inspection can catch issues like:

• Loose or worn belts

• Low refrigerant

• Electrical problems

• Dirty coils and filters

Pro Tip: Spring is the ideal time for a tune-up—before Pittsburgh’s hot and humid summer kicks in.

Change Your Air Filter Regularly

A clogged filter forces your system to work harder and can lead to:

• Whistling sounds from air restriction

• Overheating and noisy operation

• Dust buildup on components

Set a reminder: Change your filter every 1–3 months, depending on usage and whether you have pets or allergies.

Keep the Outdoor Unit Clean

Debris like twigs, leaves, and dirt can cause your condenser to rattle or buzz.

Clear a 2-foot space around the unit and hose it off gently (with the power off) a few times a year.

Don’t Ignore Small Noises

The longer a small problem goes unchecked, the more damage it can cause. If something sounds off, get it looked at—even if your home still feels cool.

When to Call Pittsburgh’s Best

If you’re in the Pittsburgh area and your AC is making strange noises, you don’t have to play guessing games. The HVAC pros at Pittsburgh’s Best Plumbing, Heating & Air are here to help with:

• Fast diagnostics and honest solutions

• Emergency AC repair services

• Seasonal tune-ups and maintenance plans

• Friendly, local technicians you can trust

Call us today 855-544-2378 or schedule online to keep your home cool—and quiet—all summer long.

Final Thoughts: Strange AC Sounds Are Your System’s SOS

Air conditioners aren’t silent machines—but they also shouldn’t be screaming, banging, or buzzing loudly. Strange sounds are almost always a sign of something going wrong, and catching them early is the best way to protect your comfort and your wallet.

Whether it’s a buzzing capacitor, a loose fan blade, or a refrigerant leak, the licensed HVAC techs at Pittsburgh’s Best can get to the bottom of it fast.

Quick Reference: AC Sounds Cheat Sheet