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NOISE – A heat pump system starts making an unusual noise. The noise may be generated from the indoor or the outdoor unit.


Typically, noises generated from the indoor unit are caused by some type of problem in the blower system.


Loose Belt

Some older furnaces use a belt-drive motor and blower system. When the belt becomes loose it can generate a squeaking or squealing (especially on start-up). A damaged belt may cause a thumping noise.

Bad Blower Bearings - Qualified Technician Recommended

Belt-drive blower systems will also have external bearings at each end of the blower shaft. A bad bearing can generate noises that range from a high-pitch squealing noise to a low-frequency thumping sound. If you suspect bad blower bearings, you should contact a qualified technician to diagnose.

Broken or Loose Blower Wheel - Qualified Technician Recommended

A common symptom with blower wheels is a noise I can only explain as a loud “V-V-V-V-V-V-V”. This is caused by blower wheel blades that have broken their weld connections and vibrate as the wheel turns. It is possible to continue operating the blower in this condition, but action should be taken to repair as soon as possible.

A broken blower wheel, on the other hand, may result in a loud clanging or banging noise from the furnace when the blower motor starts. It may also cause the furnace to shake when running. If you experience these symptoms the system should be turned “Off” and a qualified technician should diagnose.

Air Leakage

Small air leaks in the furnace or ductwork (especially on the return air side) can cause a high-pitch whistling sound. A common source is around the air filter if the filter slot is open. Covering the air leaks with duct tape will generally eliminate these noises.

Restricted Airflow

If airflow becomes blocked or restricted, the furnace blower can be put under greater strain and make noises that are louder than normal. Look for a clogged air filter or closed/blocked registers.


Typically, noises generated from the outdoor unit are caused by vibrations or metal objects coming in contact with each other. However, some noises may be caused by normal equipment operating cycles.


Defrost Cycle

When a heat pump enters a defrost cycle, the reversing valve in the outdoor unit switches to cooling mode. This will generally be accompanied by a "SWISH"ing sound. At the same time the outdoor fan motor shuts off but the compressor in the outdoor unit will continue to run. As the unit nears the end of the defrost cycle the compressor may start getting louder and steam may come out of the top of the unit. When defrost is finished, the reversing valve switches back to heating mode (another "SWISH"ing noise) and the outdoor fan restarts.

Ice build-up

If a heat pump fails to properly defrost, excess ice will build-up on the outdoor coil. This will cause unusual fan noises at the outdoor unit. It is possible for ice to build-up to the point where the outdoor fan blade comes into contact with the ice which will cause a clicking or clanging noise from the outdoor unit. If you notice an excessive build-up of ice on the outdoor unit you should switch the thermostat to "Emergency Heat" and contact a qualified technician. * Do not attempt to remove ice from the outdoor coil. Equipment damage may occur.

Sometimes as snow or ice melts off of a roof or gutter, the water can drip onto the outdoor unit and re-freeze. This ice can block the fan outlet or can come into contact with the fan blades. This will cause a clicking or clanging noise at the outdoor unit.

Fan blade out of balance

Metal fan blades can become out-of-balance and make the outdoor unit shake while running. This shaking can cause a wide variety of vibration-related noises. The unit can continue to run in this condition, but prolonged use may cause damage to critical system parts. Steps should be taken to repair as quickly as possible.

Object in the fan path

It is not unusual for foreign objects (sticks, weeds, etc.) to get through the fan screen and get in the path of the fan blade. This will cause a loud clanging sound when the unit is operating. * Do not attempt to remove anything from the fan guard while the unit is operating.

Loose screws

A common source of noise from the outdoor unit is loose panels rattling. If you can make the noise from the outdoor unit go away by putting pressure on some part of the unit, there is likely a panel or component that is not fastened securely.

Our focus and specialty is quality installation, service and repair of heating and air conditioning systems - both residential and commercial.

For more than 45 years, GHAC, Inc. has been the trusted name in HVAC for customers all across the Tri-State.

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