You should be accustomed to the sound of your HVAC system running. A low hum or the sound of blowing air is normal. If your air vents suddenly become very noisy and distracting, it’s often a sign of a more serious issue. Depending on the problem, there may be an easy or more complicated fix requiring a professional. The following is a list of reasons air vents make weird noises to help determine what to do next.

Dirty/Clogged/Old Filter

If you don’t change the air filter every 90 days, it can become clogged with dust and debris. A clogged filter can cause a high-pitched whistling, loud thumping, or buzzing sound. It can also cause the AC to cycle on and off more frequently. If the cause is a bad filter, replacing it is simple and should result in quieter air vents.

An Air Vent is Blocked or Closed

In a traditional HVAC system, closing vents can increase pressure, which in turn causes noise. Open the damper or adjust it for the right balance. Covering the vent also won’t make matters any better; it can restrict return airflow and increase motor amperage. If a vent is blocked by furniture or any other item, move it and keep the vent clear. Keeping vents unblocked and open is one of the easiest ways to reduce air vent noise.

Debris in the Ducts

Buzzing, rattling, or flapping sounds can mean debris is trapped in the air ducts and is being moved around by air currents. Even with regular filter replacement, this can happen but it means you need professional air duct cleaning.

Ducts Are Loose or Disconnected

A loose duct joint will cause metal components to flap around, resulting in clanking and rattling sounds. As a short-term fix, loose sections can be wrapped with metal tape to reconnect them. Try to tighten any loose nuts and bolts as well. However, only a professional can provide a permanent fix for loose ducts. 

A Refrigerant Leak

A hissing or bubbling noise likely means the refrigerant line is leaking. But it can mean there’s a valve leak or compressor damage as well. Don’t ignore these sounds no matter how subtle they are. A leak is a serious and possibly dangerous situation and must be fixed by a professional.

Motor Damage

You may hear a loud hum if the motor is unbalanced or failing. If there’s a lot of banging or rattling, motor parts may have become loose. Meanwhile, high-pitched squealing or screeching can mean a belt is wearing out or the motor bearing has failed.

Air Ducts Are Too Narrow

If your supply ducts aren’t wide enough, you may hear loud wooshing sounds from the vents. Narrow ducts can also be more prone to blockages by debris. When you clean noisy vents and you still hear the sounds, have a contractor evaluate your ductwork for any design issues.

High Air Velocity

Unpleasant noise can result when air moves at a higher velocity than the duct and vent were designed for. The noise will tend to be higher the stronger the air velocity. You’ll need a professional to find the cause and either make adjustments to reduce airflow or fix issues like bent or sagging ducts. They can also add ductwork, install a bypass duct, or replace or expand grilles and registers to reduce the noise.

Is the Noise Coming from My Supply or Return Vents?

Flapping noises are common from supply vents due to loose sections, but various other odd sounds may be heard. Oftentimes, they come from the blower fans. Return vents, which bring air back to the AC, furnace, or heater, can make whistling noises due to dirty filters, or knocking or banging noises due to a loose component in an HVAC unit.

Contact Sky Heating & Air Conditioning

Our team addresses a wide range of air duct issues and can, if necessary, clean, seal, or upsize ductwork. Using our Sky Seal process, we seal ductwork from the inside out and minimize air leakage. But if an air vent is making weird noises, Sky Heating & Air Conditioning has the expertise and tools to find and fix the problem fast. To learn more about our duct sealing and ductwork services in the Portland area, and schedule service, call (503) 673-9083 today.