Why Does Heat Pump Make a Loud Noise When It Shuts Off?

A lot of home appliances can be relatively noisy and that’s completely normal, in the majority of cases. But if your heat pump produces a noise that makes you jump whenever you turn the unit off, it’s definitely an issue that needs to be fixed.

The inside unit can be making a loud noise because the air filter is slamming against the grille, the ducts are expanding and contracting, and the fan’s mounts are loose. The outside unit with a broken compressor spring and a loose fan is going to be noisy as well.

Can you fix these issues on your own or would you have to call an expert to deal with the problem? You’ll find the answer (and more interesting info) below.

Why Does My Heat Pump Make a Loud Noise When It Shuts Off?

It is absolutely normal for your heat pump to make noises from time to time. Especially, during shutdown, when quite a few things happen in the system.

For example, the pressures in the refrigerant equalize right after the unit is turned off. This makes the heat pump produce some sounds for a bit.

You can also hear a ‘back-peddling’ noise coming from the outdoor unit during shutdown (if your heat pump has a certain type of compressor).

Both of these sounds are normal, but there are a few other noises that a heat pump can make during shutoff that can indicate that something is wrong.

Read: What Is Heat Pump? Everything You Need To Know

Heat Pump Noise Inside the House

If you hear a noise that sounds like someone slammed a non-existent door in the ducts, then there is definitely a problem with your heat pump.

Tip: if your unit has a damper, this component might be producing the sound, but the noise shouldn’t be too loud.

the air filter slamming against the grille.

You might experience such an issue if you have your return vents on the ceiling. At one point, the filter might get sucked up right against the top of the duct box, and once you turn the unit off, you’ll hear the sound of the filter ‘dropping’. 

This is not normal and it looks like your filter is either dirty or too restrictive.

Make sure that the MERV rating isn’t too high and replace the filter, if it’s clogged.

Also, do bear in mind that the filter will get sucked up if the ducts are too small. The only thing that you can do in such a case is install new ductwork.

The ducts are expanding and contracting.

Sheet metal ducts can expand and contract from the temperature and pressure changes. This won’t happen if your ductwork is properly sized for the amount of air circulating through the system.

There is a problem with the fan.

The blower wheel might be banging against the unit. Throughout time, the fan’s mounts can become looser – this will make the component hit the unit as it slows down.

Invite a professional to have a look at the blower wheel assembly.

Read: What Are Heat Pump Disadvantages?

Heat Pump Noise Outside the House

From outside, you might hear a noise that sounds like something had just hit the wall.

  • The compressor’s spring is broken.

A compressor is a sealed casing that has plenty of components inside responsible for pumping the refrigerant to and from the indoor part of the unit.

The majority of the components (the refrigerant pump, for example) are mounted on springs. But these supports can wear out or simply break.

As a result, the inside components of the compressor are going to knock against the casing as soon as the heat pump stops as these parts will lose momentum.

Unfortunately, if that’s the case, you would have to replace the whole compressor and that is going to cost you a small fortune. If you can ignore the sound, then you might want to do that (the noise doesn’t mean that the component is going to go bad soon).

  • The fan is knocking against the unit.

The outdoor fan can become loose as well. When that happens, the fan is going to hit other components of the heat pump once it stops operating.

The great news is that you might only have to tighten a few bolts. If the issue is a bit more serious, the whole fan might need to be replaced.

Read: What Causes A Heat Pump To Freeze Up?

What Does a Bad Heat Pump Sound Like?

We have already figured out that it is not always normal if the heat pump makes a loud noise when you decide to switch it off.

What are the other noises that you should look out for?

Metal-to-Metal Sounds

If you hear noises as if a metal object is hitting another metal thing, then the chances are high that the fan blades are hitting something.

You should immediately turn the heat pump off and inspect the unit.

The blades might be hitting an object that accidentally ended up in the unit (like a chunk of ice, for example). 

The fan might also be bumping into one of the unit’s components. At times, the blades can end up splitting the tubing through which the refrigerant flows.

In any case, shutting the unit down is the best possible decision. If you ignore the noise, the fan, the motor, or a part of the unit that the blades are touching can get damaged.

Rattling or Vibration-Like Noises

Some units rattle or vibrate while operating, so make sure to ask noise-related questions, when getting a new heat pump. 

However, if the unit never made such sounds and then suddenly started producing noises, then something has definitely changed in the system.

  • The piping for the refrigerant can be piped too tightly.
  • The metal cover panels might be a bit loose.
  • The actual air handler can have some loose parts in it.
  • It might be the ductwork that’s making a rattling sound.

Tip: you can try placing rubber mats under the unit to reduce the noise.

Read: The Most Efficient Way To Use A Heat Pump

Grinding, Buzzing, or Gurgling Noises

A low refrigerant charge might be the issue. Also, if your unit has dirty motor bearings, it can start making terrible noises that sound like shrieking. 

Coils or contactors can be producing buzzing sounds, but if the noise is not too loud, it is completely normal.

Fact: an average heat pump has a sound level between 40 and 50 decibels (sounds at these levels can’t cause any damage).

How Do I Stop My Heat Pump from Making Noise?

You can’t really get rid of all the noises that the heat pump makes and whenever you will switch the unit off, you are going to hear something.

However, there are a few tricks that you can try out to reduce the overall noise level of your system.

Use vibration isolation damper mounts.

It is normal for the compressor to vibrate. But vibration is the thing that can become the biggest problem when it comes to noise issues.

Thankfully, there are special vibration isolation damper mounts available on the market that can be installed directly on the bolts that hold the compressor in place.

The unit will still be functioning as effectively, but the noise level will be significantly reduced.

Install compressor sound blanket wraps.

Another thing that a professional could do to make your compressor much quieter is installing a sound blanket wrap. 

Such a blanket is made out of noise-reduction material and can be fitted snugly right over the compressor.

Tip: a sound blanket wrap can become a great solution if your quiet unit started becoming noisier due to age.

Use a noise-absorbing base.

This tip is pretty much straightforward. Place your unit on a special base that will lower the heat pump’s noise level. 

Relocate the heat pump.

Your comfort level will depend on where you decide to place the actual heat pump.

For example, the outdoor unit should be located away from windows.

To go the extra mile, protect the outdoor unit from high winds as those can cause defrosting problems and might make the system work at full capacity much more often. A shrub or a fence are a great fit for the job.

Replace the unit.

Remember that the average lifespan of a heat pump is 10-15 years. If your unit started making loud noises and it’s getting close to the end of its lifecycle, then it might be better to invest in a new, more energy-efficient (and quiet) heat pump. 

Read: Reasons Why Heat Pump Turns On And Off Repeatedly