Ductwork Makes Banging Noise: Causes & Solutions

homeowner covering ears due to noisy hvac ductwork

With central heating and air conditioning systems, warm or cold air is produced in one location and distributed throughout the house via ductwork. Ducts are often made of metal, making them susceptible to ductwork noise at the slightest disturbance. Homeowners might get annoyed if this becomes loud and frequent. It may even prevent people from sleeping soundly at night. Read on to learn more about why this happens and what you can do to reduce it.

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Possible Reasons Behind Ductwork Noise

HVAC ducts may produce noise due to a variety of reasons. Listen closely to identify the types of sounds being emitted. Even if you can’t see what’s causing the problem, you can get an idea from the noises that you hear. One of the most common noises we deal with is when HVAC ductwork makes a banging sound.

Ductwork Is Banging

Some homeowners report noise that sounds like something is popping and banging inside the ducts. This generally occurs in short bursts. It is caused by the expansion and contractions of the walls of the ductwork when internal temperatures change. Pressure fluctuations may also trigger this type of noise. Remember that hot air can make ducts expand, while cold air can make them contract. It may be imperceptible to the human eye, but you can hear it happen in real-time shortly after turning on the furnace or air conditioner.

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Causes For Additional Ductwork Noises

Ductwork can also produce different noises outside of banging and popping. Here are some common ones and their causes.

Rattling Ductwork

image of rattling ductwork

If you hear rattling from inside of the air ducts, then there is a good chance that the culprits are loose metal parts. They make noise when they knock against each other. This tends to happen as ductwork ages. The seals begin to fail and the connections become loose due to the static pressure. The sound will be present for as long as air moves around the ducts. It may start off as a soft sound, but it will get louder with time until you cannot ignore it anymore. Get help from HVAC professionals in finding and fixing the problem.

Booming HVAC Ductwork

This is a loud sound that you may hear at the junction of the duct’s trunk and the plenum. The spot experiences the biggest swing in temperature. If the connection has an inadequate amount of expansion joints or dampers, then the noise will reverberate around the house through the supply ducts. Skilled and experienced installers know that this can happen, so they do everything they can to reduce the noise from the connection.

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HVAC Ductwork Is Shaking

Sometimes you may hear and see the ducts shaking or vibrating with a low hum. This often occurs when the return side’s airflow is blocked because of a dirty filter. Since air cannot enter, the pressure drops so low that the duct walls begin to shake and vibrate. Make it a habit to check on the condition of the air filters. If it is beginning to get too dirty, then clean it up or replace it with a new one. The ducts will operate more quietly and the system will maintain its high efficiency.

Scratching Ductwork

image of a rat infestation and rat inside ductwork

This is another unwelcome type of sound coming from the air ducts. If it seems like something is scratching the metal walls, then there is a good chance that rats, raccoons, squirrels, and other creatures were able to enter the system. Act immediately or they might create a nest and make it their home, negatively affecting air quality. If you hear buzzing noise, then that might be due to the wings of a bee or other large insects that are trapped inside. Call an HVAC contractor for help.

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How to Reduce HVAC Ductwork Noise

Homeowners don’t have to deal with the noise forever. Creatures and foreign objects can be removed from the ductwork. Problem areas can be repaired by competent HVAC technicians. As for the noise triggered by normal operation, it is possible to reduce the loudness and make them bearable for those who want a quiet home. Below are some practice solutions that you can employ to make this happen:

Adjust The Fan Speed

Installers configure the volume of airflow at the outset. There is an optimum range for each system after accounting for multiple factors. Often, they set the speed too high. If this is the case in your home, then you can lower the fan speed to lessen static pressure. You may want to seek the help of an HVAC professional with this because setting the fan speed too low can make it hard for conditioned air to reach certain rooms.

Change the Air Filters

image of dirt on air conditioner air filter

Always keep your eye on the filters. These are meant to catch dirt while allowing air to pass through. The more dirt they catch, the harder it is for air to breach the barrier. These need to be replaced every 2-3 months to maintain good airflow and efficiency. However, some homes with pets and in dusty locations may require a monthly replacement. The frequency depends on your home in particular. A clean filter prevents banging and popping sounds from the ducts. Air filters are relatively cheap, so get them right away and help your HVAC system perform better.

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Install Larger Ducts

Consider the possibility that your ducts are too small to handle the volume of air that the system needs to work well. Although your actual heating and cooling units are of the correct size, there will still be problems if the duct is undersized. Discuss this with your HVAC contractor so that they can study the matter. Larger ducts help in reducing the noise, as does a larger return and supply plenum. Pair these with high-velocity grills and registers to improve airflow.

Add a Bypass Duct

If there is a lot of pressure in a multi-zone system, then use a bypass duct to lower it. Reducing the pressure is a great way to remove excess stress on the ductwork and prevent common issues. However, it will only be effective in certain cases. Consult HVAC professionals to see whether this option is a good match for your ducts.

Try a Different Duct Shape

image of hvac ductwork repair by an hvac contractor

If you are going to install new ducts, then consider the shape. Rectangular ones are popular because of their slim profile and clean lines. However, they tend to produce more noise than round ducts because of lower pressure tolerance. If the latter can fit in your home, then it may be worth a look. Talk to a local HVAC company.

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Use a Duct Silencer

A duct muffler may be installed for round ducts to further reduce the noise they produce. These have a double-wall design and built-in insulation to dampen the vibrations. These work best when installed near the air handling unit, fan, and other components that make the most noise. Note that these can only reduce unwanted sounds. They cannot eliminate them completely.


Insulate the Ducts

Insulation can be wrapped around the ducts to improve their energy efficiency. This will also help in keeping the noise down, particularly with the banging and popping sounds. Let a certified technician perform this task for the best results.

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Switch to a Ductless System

If you have already done the noise reduction strategies above but remain unsatisfied, then perhaps you should move away from ducts altogether. Consider switching to a ductless mini-split system to be completely free from ductwork noise and maintenance. This even comes with perks such as the ability to create multiple zones, independent temperature control, and higher energy efficiency.



Noise in the ductwork can mean a lot of things. Sometimes it indicates an underlying problem such as pest infestation, incorrect system configuration, or loose connections. In these cases, the noise is a great way to alert a homeowner about a problem that needs attention. However, noise can also be part of the regular operation of the system. It may not go away, but different strategies can reduce the loudness and frequency. Talk to your HVAC contractor to figure out the best solutions for your system.

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