How to Interpret Duct Noises

A man looks at ductwork in a ceiling.

Homes are full of noises from creaks and squeaks to moans and groans. When the noises include rattling, hissing, huffing, and puffing, it’s time to find out what is going on with the duct work.

Factors Affecting Duct Work Noises

Several factors play a role in noises emanating from the ducts in your home. These include the size, shape, gauge rating of the ducts, and the system itself.

Sizing of ducts is important if you want to keep noise to a minimum. When ductwork is installed that is too small, it causes the ducts to expand because of the pressure created by the system.

The shape of the ducts can be square, rectangular, or round, with round providing the most noise-free environment and rectangular being the noisiest.

Gauge ratings are used to rate the strength of metal ducts. In this case, a lower gauge rating means the metal is strong. This means the ductwork can handle temperature changes and pressure more effectively.

When a new system is installed, it can create a problem or two with unwanted noises. This is generally due to incompatibility between the new system and the old duct work. This may require a system check to find out what needs to be replaced to make the new and old systems function together.



Age takes a toll on ductwork. When you hear rattling sounds, it could be that the seals supporting the metal ducts have failed, resulting in a tin-type metallic noise.

Bad Vibrations

When ductwork is dealing with a clogged filter, bad vibrations are the result. A filter filled with dust and other particles prevents an efficient airflow. This causes the pressure within the ducts to drop, which leads to the knocking and vibrating sounds.


If any of the tape supporting the ducts have become loose, the air flowing through the ducts will cause the tape to flap in the breeze.

Wildlife and Insect Sounds

A man looks at ductwork.

Don’t think wildlife and insects can’t play a role in noises. If there is any damage to the ducts, such as a hole or tear, wildlife such as squirrels, rats, and possums can rip the duct and make a nest inside. Insects such as bees will also set up a nest inside the ducts. Both will result in chewing, scratching, squeaking, or buzzing noises.

Hiss, Boom, Bang

A series of events can create any or all of these noises at one time. As the temperature of the air adjusts (expands and contracts) as it travels through the ducts, it can cause the ducts to move. Another issue involving temperature changes include the dampers that filter noise. If these are damaged or inadequate to do the job, expect to hear a “boom” type noise.

At the end of the day, it’s always best to determine the cause of unfamiliar or persistent noises. Sometimes the noise is an indication of a potentially costly problem. Other times, it may be a simple fix before it turns into a much bigger problem.