Why Is My AC Making A Loud Noise When Starting Or Shutting Off?

Written By: Alexis Bennett

Edited by: Andrew Dunn

Has your air conditioner recently started making a loud noise when starting or shutting off? Are you wondering what could be causing it? If so, we can help. 

In this troubleshooting guide, we cover:

• What causes your air conditioner to make loud noises when starting up?
• Is the sound your AC is making a sign that your system needs a tune-up?
• How can you keep your air conditioner from making loud noises?
• Should you stop using your AC unit if it makes a loud sound?

Any time you hear a strange sound coming from your HVAC it can instantly invoke anxiety, especially during the hot summer months or when you have a high-risk person living in your home. 

We have been there, too. So, do not worry. 

We will help you troubleshoot the sound, and if it is something significant, we have a tip for dealing with that too.

What Are The Most Common Causes Of Loud Noises Coming From Your HVAC? 

Air conditioning systems are complex and they have several dozen components that all have to work together for the process to be a success. All of those parts can wear on each other and when one or more component gives, your unit can begin making some pretty awful sounds.

There is a plus side, by listening closely to the sound your unit is making, you may be able to diagnose the issue without having to pay an expensive service bill.

Rattling Noises And Humming Noises 

Loose parts can make a rattling or humming sound. Due to the vibration in your AC unit, it is not uncommon for parts to come loose. 

However, you should fix loose parts as soon as you notice them. Otherwise, they may damage other components turning a simple DIY fix into a costly HVAC repair.

Squealing Noises And Buzzing Noise

Anytime you hear buzzing coming from an electric-powered appliance, it could be a sign of serious electrical problems. Your air conditioner usually makes this sound when the voltage is too low, wires have come unsoldered, your compressor motor is no good, or you have a bad run capacitor, you may hear a buzzing noise coming from your air conditioner.  

An improperly seated air filter can also cause a rattling sound inside when you start up your unit or power it off.

Banging Sounds And Slamming Noises In Your House

A slamming sound or banging noise, clanking, or clanging, could be your AC system’s damper closing when your system shuts off. The sound is usually very brief and it may sound like two pieces of sheet metal clashing together.

A Clanking Noise In Your Air Vent

If the blower motor connected to your heat pump is no good, you may hear a light thud or clanking coming from your air vent. The noise you hear could be a result of the blower wheel hitting another component or something foreign in your HVAC.

Cracking And Creaking Sounds Coming From Ductwork

When your air conditioner turns on and shuts off, it is not uncommon for airflow or pressure to make the ductwork and other flexible parts creak and crack. Cracking sounds are usually nothing to concern yourself with unless you hear a crack followed by a thud. 

The air ducts and other flexible components may also creak and crack as the temperature changes. While it is not an incredibly loud sound, it can be startling because it sounds like your building is cracking.  

You Air Conditioner Makes Clicking Noises 

Like buzzing and humming, a clicking noise either when the system is on or off could mean you have a major electrical connection issue. The unit clicks because it is attempting to turn on. 

To avoid calling an HVAC technician for a simple fix, make sure that none of the breakers are tripped. If a circuit is tripped, at least part of the unit will not be functioning.

What Should You Do If You Hear A Loud Noise Coming From Your AC? 

A loud noise coming from your outside unit means you likely have a broken compressor, run capacitor, or condenser fan motor. Each of those components is vital. 

If one or more is not functioning, it will cause warm air to come out of your air vents, and if you leave the components unfixed, they could compromise other parts, too. So, here are a few steps you can take to troubleshoot your air conditioning unit. 

1. Check The Outdoor Fan And Inspect The Unit

Your condenser fan is the giant blades that are in the center of your outside unit. Before you adjust the thermostat or start troubleshooting, you should check to see if the fan is rotating, and if it is, observe how the blades are spinning. 

If they seem to be off-balanced or you hear the fan hitting something, debris in the condenser casing could be responsible for the sound you hear. If you do not see anything hitting the fan, check to see if the coil appears to be in good condition, and check the copper refrigerant piping at the base of the unit for ice. 

If there is ice on your unit, it means your HVAC system freon levels are low and there is likely a refrigerant leak.