Why Is My Heat Pump Making Humming and Other Loud Noises?

If you are outside near your heat pump and you notice it making a humming noise or any other loud type of noise do not be alarmed. You don’t have to run away thinking it’s going to blow up.

But you should consider a few things because your heat pump may need some service work.

That’s why we have taken the time to write this article. In it, we will discuss some common heat pump noises and tell you whether or not those noises could lead to a bigger problem or it’s something you may even be able to simply correct yourself.

Are heat pumps considered to be a loud device? The answer to that question is no. Normal sound levels emitted from most heat pumps range between 40 and 50 decibels. That’s less than a working dishwasher or a light rainfall.

That’s why it’s so important to investigate loud noises if they are noises you are not used to hearing them make.

Learn Your Heat Pump’s Normal Operating Sounds

To tell you the truth, if you are a homeowner it’s a great idea to familiarize yourself with the typical noises your heat pump makes when running. Then if you start hearing sounds you don’t recognize coming from your heat pump system, it will alert you to the fact that there may be a problem.

So take a little time out to get acquainted with your heat pumps normal operating noises.

4 Usual Heat Pump Noises

Before we get started on some of the heat pump noises that you really have to worry about, let’s first go over some common heat pump noises that are indicative of a properly running heat pump.

Heat pumps are a mechanical device with a few moving parts such as fans that do produce some noise when running. They also create sounds when the refrigerant found inside them changes from a liquid state to a gas. So some noise when your heat pump is running is considered very normal.

What are some of these so-called good noises that come from a heat pump unit that is nothing to be concerned about? Here are a few of them explained:

Startup and Shutdown Noises

Most people do not hear the sounds their heat pump makes when it comes on or shuts down. That’s because when your heat pump is installed it’s strategically placed in an area outside your home where its operating noises disturb you the least.

Some compressor units on heat pumps will make a sound like an ‘out of balance washing machine’ when they first start up. This noise can be quite loud but should only last a few minutes. When a heat pump shuts down there is also some noise associated with this process too. Some people describe this noise as a combination of loud ‘clicking and tapping’. Once again this noise should go away after the heat pump is running a few minutes.

Defrost Mode

One of the byproducts that’s created when your heat pump is moving warm air into your home is excess cooled air around the outside of your heat pump unit. Eventually, your heat pumps evaporator coils will start to freeze over. When this happens your heat pump will be less efficient or not transfer heat at all. This is a normal part of heat pump operation.

When the frost buildup on your evaporator coils gets to be too much your heat pump will sense this and automatically switch itself into defrost mode for several minutes. This is often accompanied by a loud ‘swooshing’ sound for a few minutes when your heat pump switches over into this defrost mode.

Gentle Humming/Buzzing

Don’t be alarmed if your heat pump makes a gentle humming noise as it operates. This is something that is perfectly normal. There are a number of internal electrical components in your heat pump such as coils and contactors that are known to quietly hum or gently buzz as they are transferring electricity through them.

Fan Motor Noise

Air is the key to how your heat pump transfers heat into and out of your home. This air movement is created by a large fan located at the very top of your heat pump. When it runs it can be a little noisy but nothing that’s bothersome. The noise your heat pump fan produces should be consistent, smooth and not overly loud. You may also hear a click just before your heat pump fan comes on.

Bothersome Heat Pump Noises and How to Troubleshoot Them

Interior Whistling Noise

This will typically happen on the inside of your house when your heat pump unit is running. Usually, a whistling sound is created when air is rushing quickly through a small opening. This is usually caused by such things as dirty air filters on your system or from objects being placed in front of air registers and vents that restricts the airflow going in or out of them.

TROUBLESHOOTING:
This heat pump system noise is usually pretty easy to correct. Simply cleaning or replacing your air filters on a routine basis will keep it from ever happening on the air intake side. Also try to remove any furniture, boxes or other objects that are cutting down air flow through vents or registers.

Rattling Noises at the Unit or in the Air Duct System

If you hear rattling noises coming from the heat pump unit it usually means that some debris has fallen into the fan area. This is quite common if you have many big trees in the yard near heat pump or there have recently been strong winds in the area. Dead branches, leaves and other debris will make a rattling or clanking noise when the fan blades of the heat pump unit contact them.

Any large debris that gets trapped inside your air ducts can make a rattling noise too as it bounces around in them. Having your filters properly in place at all times should prevent debris from being sucked in the ductwork but not always.

TROUBLESHOOTING:
Before you attempt to get debris out from your fan area to stop a rattling noise always be safe and make sure you ‘SHUT THE UNIT DOWN FIRST’. Then just carefully remove the debris from around the fan blades. You may have to take off the protective screen that covers the fan to get this debris out of the unit.
To clean debris out of the systems air ducts is a little trickier. That’s because it may be hard to locate the debris. Try to pinpoint where the rattling noise is coming from inside the air duct system then shut down the heat pump and try to remove the debris. You may have to remove a register cover or vent cover to get to the debris. If you are not successfully locating the noise causing debris, then call an HVAC professional to come to get it out for you.

Metal on Metal Sound near the Unit

This most likely is the result of bent fan blades on the heat pump’s fan or somehow the fan has come out of alignment causing it to come into contact with another metal area on the heat pump. Over time this will ruin either the fan blades or the fan motor itself. Not to mention this noise will probably be so loud it will annoy you even inside your home.

TROUBLESHOOTING:
There is a 50/50 chance you can correct this heat pump noise problem on your own. Do this by taking off the fan motors protective screen first. Then tighten down any screws or nuts which may have come loose causing the fan unit to tilt slightly. If the problem is a bent fan blade try gently straightening it. If this does not work you can buy a new fan blade and replace it yourself. If none of these correct the fan blade from hitting on metal you will need to schedule an HVAC service call.

Vibration

Any vibrating sound coming from your heat pump is not your friend. Vibrations do such things as loosen screws and nuts on bolts. If left uncorrected for long periods of time vibrations can even cause much bigger part failures. The louder the vibrations the more serious they are.

TROUBLESHOOTING:
Most vibrations can be taken care of by you even if you have limited mechanical aptitude. Try and locate the loose piece of equipment which is causing the vibrating noise. Once you find it, tighten down any screws or nuts that are meant to secure it in place. A little piece of strategically placed rubber does wonders for stopping vibrations too.

Loud Humming

Unusually loud humming coming from inside your heat pump is not normal unlike the gentle humming we discussed earlier. This will most likely be caused by one of the electrical components inside your heat pump becoming worn out or not stopping making an electric connection when they are supposed to. A seized fan motor will also create a very noticeable loud humming noise.

TROUBLESHOOTING:
If you have an electrical component that is humming loudly it will need to be replaced. If you know how to do electrical work you may be able to do this yourself (remember to always turn off the power before working on your heat pump’s electrical system). Having a trained HVAC tech do this work is probably best though.

Hissing

If there is a hissing sound coming from either your heat pump unit or from your ductwork this is never a good sign. That means air, or even worse yet refrigerant, is escaping from your heat pump system and that is never a good thing. Once your refrigerant gets low your heat pump will no longer be able to transfer heat from inside or outside of your home.

TROUBLESHOOTING:
Unfortunately, unless you know heating and refrigeration systems well you will not be able to troubleshoot this problem yourself. If you hear hissing coming from your heat pump unit, shut it down and call for HVAC service.

Repeated Gurgling Noises

The refrigerant inside your heat pump changes from liquid to gas depending on where it’s at as it cycles through the pressurized lines in your heat pump. In order for your heat pump to work properly, this refrigerant level has to remain fairly constant. Small leaks in the pressurized lines in your heat pump can cause refrigerant loss over time. When this happens it may produce gurgling sounds in the pressurized lines as the system runs.

TROUBLESHOOTING:
Fixing refrigerant leaks and adding more refrigerant are jobs for a trained HVAC professional. It’s time to schedule an HVAC service call if you continually hear gurgling noises in your heat pump and it seems not to be working efficiently.

Loud Shrieking When the Fan Motor is Running

Your heat pump fan blades are able to turn because they are attached to a powerful electric motor. Unfortunately, this sealed electric motor is somewhat out in the open. Over time it can start to get some moisture inside of it. Eventually, this moisture will begin to promote breakdown of the oils that keep the motor bearings lubricated. Once this happens the ‘shrieking noise’ the un-oiled bearings will make can be very irritating to say the least.

TROUBLESHOOTING:
The only way to stop the shrieking sound coming from your heat pump’s fan motor is to replace that motor. This is a job best left to a professional HVAC tech.

Regular Heat Pump Maintenance Is Always Recommended

So now you should know much better if the sounds that are coming from your heat pump system are normal or something that you should be concerned about. Remember, if any noise that comes from your heat pump system is very loud and abnormal you should immediately shut it down and call a professional HVAC tech. It’s never a bad idea to have your heat pump serviced on an annual basis either. Regular maintenance service and listening for abnormal heat pump noises can go a long way toward helping you extend your heat pump’s useful life.

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