Heat Pump Noise - Detect Early Signs!

Detecting heat pump noise can turn an expensive future expense into a less expensive fix right now.

This page is not meant to address every possible noise coming from a heat pump. Each model and each manufacturer is a little different...so the troublesome noises will be different.

But....there are many common noises that originate from the components of a heat pump. Please keep in mind that diagnosing a noise using words is very subjective and is open to much interpretation. So this is merely a guide to help narrow down the possibilities.


Please share with us the heat pump noise that you encountered
(and the solution, if you have it!)


First, let's talk about the heat pump noise encountered during the defrost cycle. This is commonly mistaken to be a problem, when in reality, it is very normal.

Watch and listen to the video below. The noise encountered when the fan stops is the normal sound emitted during the defrost cycle:

Now let's discuss some common noises that could be the first sign of a problem.

Noise #1: Humming or buzzing at the outdoor unit

Humming is a very common noise that originates from the outdoor unit, especially when it is not able to run.

Humming often indicates a

  • stuck relay or contactor
  • a faulty capacitor
  • a motor that will not spin. This situation should be remedied as soon as possible. The motor is at risk for overheating. Remember that there are two motors in the outdoor unit of a heat pump; the compressor and fan/pump motors.

Noise #2: Tumbling rocks/pebbles or popcorn popping

I know that description sounds strange but this is often the description given when a compressor is receiving liquid refrigerant. The louder it is, the more liquid it is receiving. This problem is one that should not be ignored. There are many potential causes for liquid refrigerant slugging and a service technician will need to go through the diagnosis process.

Noise #3: High pitched squeal

Screw compressors are often high pitched, especially at start-up. So if the system has "always" had the high pitched squeal, chances are this is typical. However if you had never noticed it before, this could be an early indication of a motor going bad.

Noise #4: Loud metallic banging

Potential causes for a loud and frequent metallic banging is:

  • Worn compressor bearings
  • Loose motor mounts

Noise #5: Loud non-metallic banging

The difference between Noise #4 and #5 could be insignificant. Depending on what you interpret as a "metallic" sound could be the difference in diagnosis. So it is very possible that the causes above could apply to this section as well (and vice versa).

Noise #6: Hissing

A hissing heat pump noise is almost always a refrigerant leak. A refrigerant leak that can be heard is quite large and it will result in a "flat" unit in a short amount of time. So this must be remedied quickly.

Noise #7: Rattling (low volume, cyclical)

Just like noises #4 and #5, is the pitch of the rattling low or does it have a high pitched metallic sound?

Does it sound like it is coming from the compressor or another part of the unit?

Some possibilities are:

  • Loose piston rod on a reciprocating compressor
  • Loose hardware
  • Liquid slugging (a common, but undesirable occurrence at start-up)

Noise #8: Screaming (high volume, high pitch)

The diagnosis for heat pump noise that has an uncomfortably loud, high pitch sound almost always goes back to the compressor.

If it is high pitched this could be a dangerous situation for both the equipment and any people involved. This could indicate that the compressor is pressurizing the refrigerant to an abnormally large differential pressure. Very carefully record the actual pressures and shut it down as soon as possible. If there is concern regarding the operational safety of the equipment shut it down immediately.

Noise #9: Labored sound (high volume, low pitch)

Sometimes there is nothing abnormal about a loud low-pitched noise. However if it is louder than it used to be, this could indicate some problems, such as:

  • Improper refrigerant charge
  • Improper oil level
  • Compressor near the end of its life

Of course, noises can be difficult to describe with words. If this webpage didn't give you the answer you are looking for, try to listen for your heat pump noise.



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