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Noisy Air Vents, High-Pitched Noise

Noisy Air Vents, High-Pitched Noise:

All air conditioning vents generate some noise when the system is running. This is normal. Some a/c systems are louder than others. Some a/c systems are much louder than others.

For example; a house with a good amount of return air vents is going to be quieter when compared to a system with just one single large return grille cut straight into the return duct of the a/c unit. There is nothing technically incorrect with the latter, it is merely a more affordable system to set up and is an extremely basic method of ducting the equipment. The downside of course is that it could be loud!

The most common complaint we get on this matter is often from return vents making a high-pitched, tuning-fork kind of sound. This usually, not necessarily, but usually, indicates too little return air. The a/c system must pull more air therefore the pressure and velocity rises, thus increasing the audio level. With the addition of more return air, the pressure drops, the machine doesn't stress, and it quiets down.

Now, why is there not enough return air? The ductwork could possibly be undersized or not installed properly. But it may be as simple as a blocked air conditioning filter. Someone closed off way too many vents maybe. This could cause the condition as well. A central air conditioning system is designed to move a certain amount of air (measured in tonnage). By blocking either the supply or return vents, (whatever restricts the airflow) it causes a pressure problem - increasing the sound level. We've seen furniture blocking return vents, restricting ventilation.

Other vent-related noises incorporate rattling and or flapping noises - which usually are due to particles in the duct... screws, nails, small toys, plastic material, construction materials, saw dirt, etc. So after checking all of the apparent things, the next phase would be to include a technician inspection the system's performance.

United A/C & Refrigeration's service professionals will not only check the a/c system’s equipment, but can inspect the ductwork for appropriate air-flow. Along with a/c system pressures and temperature differential splits, they can look for appropriate CFM and static pressures to identify if the ac unit is moving the air in your home properly.

Below is a set of possible causes for noisy air vents and or high-pitched noises coming from your air conditioning system. Items in red need a service call by a professional, which we will be happy to assist you with. Items in blue however could be addressed, some fixed by the home owner even.

Professional Fix Homeowner Fix
  • Undersized ductwork
  • Restricted ductwork
  • Faulty grille
  • Large return very close to unit
  • Debris in ducts - may need professional duct cleaning
  • Filter blocked by furniture
  • Return vents blocked or shut off
  • Supply vents blocked or shut off
  • Dampers shut off

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