8 common HVAC noises and their reasons

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Is your HVAC unit making some unusual noises? Are the noises loud enough to distract you? If yes, then it is time to notice the noise more carefully and understand its source and reasons. Though your HVAC system is designed to work silently, it is just a system and sounds are normal and natural. But, some noises are not natural and when you hear them, it is a sign that your HVAC needs some attention. Here we will discuss 8 common HVAC noises and their reasons. 

8 common HVAC noises

Let us have a look at the 8 common HVAC noises and their reasons in detail.


If you hear a banging noise coming from your air conditioner inside your house, it may be because of problems with the compressor or the blower fan. In case the banging noise is coming from your HVAC system’s outside unit, then the reason may be a broken or loose part such as rod, fan blade, piston, etc. It may also be because of a faulty compressor. The blower fan and compressor are crucial components of your HVAC system as they are responsible for removing the excess heat from your home.


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Sometimes a loud screeching noise or a metal-on-metal noise may come from your HVAC unit, either from the inside unit or from the outside unit, which is an indicator of issues with the components. If the noise is coming from the inside unit, it may be because of a bad blower motor bearing or a worn blower belt. Whereas, when you hear the screeching noise coming from the outside unit of your HVAC, it may be because of a faulty fan motor or compressor. 


The humming noise from your HVAC unit is an indication of loose or broken components specifically condenser fan motor or contactor relay switch. When the condenser fan motor is unable to spin even after receiving enough power, it makes a humming noise. The contactor relay switch is responsible for starting the outside condenser unit, and when it fails to perform its function due to some electrical or mechanical breakdown, it produces a humming sound. 


If your HVAC starts making loud buzzing noises, keep the system turned off and take immediate action to get it fixed. The buzzing sound may be a sign of some serious issue and the following are some reasons that cause such noises:

  1. Loose fan motor
  2. Defective air filter
  3. Loose or unbalanced fan blades in the outside condenser unit
  4. Dirty condenser coils
  5. Obstruction near the copper lines connected to your system
  6. Refrigerant leak
  7. Debris
  8. Loose components
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In case your HVAC system makes rattling noises, it’s a sign that your system is not functioning as it is supposed to. Some reasons behind this issue may be:

  1. Debris in the outside unit such as leaves or twig
  2. Detached or damaged panels
  3. Damaged motor
  4. Loose or damaged fan blade


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HVAC units can make clicking sounds due to a damaged capacitor or issues with the electrical connection of your unit. Though if you hear the clicking sound when you turn on or off the unit it is normal. But, if the noise is frequent and loud when the unit is running, it is a matter of concern. If not fixed as soon as possible, it can cause serious problems to your HVAC unit, even electrical failures. Don’t use your HVAC when you hear clicking sounds coming from it.

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The hissing sound coming from the HVAC unit is mainly due to a leak in the air duct. This air leak can happen when the air filter is not set right or when the filter is of the wrong size for your unit. There may be some other reasons behind the hissing sound such as a malfunctioning valve, refrigerant line leak, or high pressure on the compressor. Whatever be the reason, it should be fixed immediately as it impacts the performance and efficiency of your HVAC unit.


If you notice any bubbling or a gurgling sound coming from your HVAC unit when it’s on, it may be caused due to issues with the refrigerant or drainage line. This problem mainly arises when the drainage pipe is either blocked or cracked or has holes in it. The damaged drainage line allows the air to be trapped in the liquid coolant lines. You can repair the drainage line on your own but it is not normally advised as you need some specific tools and skills to do it. 

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How to fix HVAC noise problems?

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Whenever you notice that your HVAC system is making some unusual and loud noises, it is recommended to turn off the unit immediately and then consult an expert or technician to fix the problem. Most of the noise issues are caused due to issues with the compressor of the unit, and it is not made for easy disassembling. Therefore, do not try to disassemble or repair the unit on your own as even a minor mistake and miscalculation can cause severe and sometimes permanent damage to the unit. The technicians have certain specific skills and tools that are required to do this type of job. Find the best technician for your HVAC unit and enjoy its prolonged and efficient performance.

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