Various AC Noises and What They Might Mean

“Why is my AC making Noise?”

Woman Investigates AC Noise

Today’s air conditioners are quieter than ever. And we want to make sure yours stays that way. High-efficiency AC units incorporate sound-dampening technology and two-stage (variable speed) compressors to keep noise levels below 55 decibels. So when you hear unfamiliar or exceptionally loud noises from your air conditioner, take notice. 

Ignoring the mysterious noises from your AC can turn minor issues into major expenses, as these noises could signal anything from needing a simple tune up to costly repairs, to — worst case — replacement of the entire unit. The sooner you can determine the cause of the noise and resolve your AC issues, the better.

Here are some of the common sounds your HVAC system could make and what they may signify.

1. AC Banging Noise

Banging is usually a sure sign that there’s a loose or broken part — a connecting rod, piston pin or crankshaft — inside the air conditioning compressor. Or perhaps, your indoor blower is unbalanced. A banging noise may also indicate that your system needs a compressor replacement.

2. AC Clanking Noise

Clanking is another sign of a loose or out-of-balance part. The parts inside the sealed unit have likely failed, and the compressor itself may have become loose, possibly necessitating a replacement. This sound can also mean that the indoor blower or outdoor fan and its blades are out of balance and hitting other parts. These types of issues will only get worse and create bigger problems, if ignored.

3. AC Clicking Noise

The clicking of electrical components at start-up and shutdown is a normal part of the system’s operation, but constant or ongoing clicking is not typical. It could be a sign of a defective control or a failing thermostat. There are a lot of electrical parts in your unit, so it’s critical to pay attention to potential electrical issues as soon as possible before you have bigger issues on your hand. 

4. AC Buzzing Noise

A buzzing noise from your outside unit could mean:
  • Loose parts
  • Debris in either the indoor or outdoor unit
  • Outdoor fan motor is loose or about to fail
  • Fan blades are loose or out of balance
  • The copper lines from outside to inside are rubbing against something
  • The condenser coil needs to be cleaned
  • The air filter needs to be changed
  • The blower is going bad or out of balance
  • Refrigerant leaks, resulting in your air conditioning freezing up. If it’s conditioning not cooling, this could be why.

If your A/C unit seems to be running outside but isn’t cooling inside, the problem is likely a refrigerant leak. This may or may not be accompanied by any telltale noises, depending on how bad the leak is and where it’s located.

5. AC Squealing Noise

Blower and fan noises such as squeaks, squeals and rattles may be transmitted through the duct system. Outdoor fan motors and indoor blower motors squeal loudly when they’re going bad. The blower wheel and housing will also squeal when they malfunction. For some units, this sound is normal upon start-up. You should be able to identify whether it’s a sound that the unit always makes or if it's something new.

6. AC Humming Noise

A humming sound generally isn’t serious, but it still signals that something inside your air conditioner is off. Loose parts and refrigerant piping can cause vibration and, if left unchecked, can lead to a more serious maintenance issue. Sometimes humming or buzzing noises point to electrical problems. If the compressor hums and refuses to start, there may be an issue with the motor, though loose wiring could trigger this noise, too. 

7. AC Chattering/Rattling Noise

A rattling noise can mean that your air conditioner is starting to deteriorate, and some of its parts are loosening. Another cause could be twigs or leaves that have clogged your system. The electrical contractor in the equipment can also make a chattering sound, which can damage other components including the compressor if allowed to continue. Another culprit could be the fan, which rattles when loose. Your first line of defense is to check for loose screws or bolts in the unit’s casing, clean condenser coils and change your indoor air filter. 

8. AC Screaming Noise

If you hear high-pitched whistling or screaming, shut the air conditioner off and call a professional right away. The most likely cause is a refrigerant leak, which not only damages your air conditioner but can also threaten your family’s health. Screaming might also indicate high internal pressure within your compressor, which is very dangerous. If your air conditioner turns off on its own, don't panic. Consider this a good thing. A sensor is doing its job to protect you from a potentially hazardous situation.

9. AC Pulsating Noise

An air conditioner making a pulsating noise isn’t necessarily a bad sign — a little pulsing noise can be perfectly normal when the air conditioner is operating. But if your outdoor A/C unit is making a pulsating noise that you can hear from inside the house, it could be a sign that something has come loose inside the unit and needs to be replaced. Some likely culprits include the fan motor and blades, but any loose panel or part could cause a pulsing noise in your AC.

10. AC Whirring Noise

If your AC sounds like a helicopter, you could have one of any number of mechanical problems with either the indoor blower or the outdoor unit. Typically, a whirring sound in an AC is the result of bad bearings in the indoor blower fan motor, or a faulty fan in either the indoor blower unit or outdoor unit. When the blades start to come loose or the fan otherwise starts to fall apart, a whirring, helicopter-ish noise can occur. There might also be a bad or broken belt somewhere in the system. 

However, the problem isn’t always a faulty part. Sometimes, a piece of paper or other debris can get trapped in either the indoor blower fan or the outdoor fan unit, causing a rapid, helicopter-blade-like whirring noise.

Investigating Weird Air Conditioner Noises

If your air conditioner suddenly starts making an unusual noise, you may want to investigate before calling for a service professional. Sometimes you can do a DIY service on your outdoor air conditioner unit to address the source of weird noises. For example, leaves, tree fluff and seed pods can easily clog up an outdoor condenser’s coils, straining the system and perhaps causing pulsing, buzzing or reduced cooling capacity. 

You can remove the top of your outdoor A/C unit to check for loose fan blades. Clean the inside and outside of the unit with a hose and a soft-bristled brush. Check and change the filter. 

If you hear something unsettling that you believe could indicate an issue with your AC, it’s a good idea to turn off your central air conditioner unit as a precaution until it can be inspected thoroughly, whether you’re going to take a look at it yourself or call for professional service right away. Air conditioning units cost a lot to repair and replace, and allowing a broken air conditioner to keep running could compound the problem. And while it’s never convenient to have a broken air conditioner, a yearly inspection and tune-up can prevent future problems.

How to reduce AC noise inside?

If a service professional finds nothing wrong with your air conditioner, or you’re just looking for ways to muffle the sound of a newly installed unit, you have a couple of options for getting rid of the aircon noise.

One such option is a sound blanket. In most new air conditioners, the bulk of the noise comes from the compressor. You can remove the top of your A/C outdoor unit and install a sound blanket over the compressor — it just sits right on top of it. This will muffle much of the sound of the unit.

Another option is to install some sound-dampening fencing around your A/C unit. This can also hide the outdoor component, as well, which many homeowners find aesthetically pleasing. For sound dampening, you should use a fencing material with overlapping boards. Make sure to place the fence at least three feet away from the air conditioner, so it can get the airflow it needs to work properly. 

You can also plant some shrubs around the AC, but you’ll need to keep them carefully pruned back. To block sounds inside your home, place some large houseplants in front of the windows on the side of the house facing the AC, and install noise-blocking curtains in your family’s bedrooms, at least if they’re on the same side of the house as the outdoor AC unit.

When to Replace a Noisy Air Conditioner?

If your unit is getting older, the best solution may be to simply replace it. Excessive noise from an older unit is usually a sign of its age, and may indicate serious problems like refrigerant leaks or a faulty compressor. Now that R22 refrigerant has been replaced by R410-A, adding refrigerant to an old system has become expensive enough to warrant replacement of the system. A compressor replacement, too, is costly enough that replacing the entire air conditioner is more cost-effective.

A new air conditioner will be much quieter, and more efficient, too. You could save enough in power bills that your AC could pay for itself in a few years. If your old air conditioner has broken down and your third-party service professional recommends replacing it, your American Home Shield home warranty could offset some or all of the costs of installing a new, more efficient, more reliable and quieter A/C.

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AHS assumes no responsibility, and specifically disclaims all liability, for your use of any and all information contained herein.

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