The 5 Most Common Reasons Your Furnace is Making Loud Noises

Is your furnace screaming for help? There’s a certain amount of noise that furnaces normally make—like a light hum or a quiet rumbling. This may be slightly more pronounced in older models, but if your furnace is making loud noises, that’s a good sign there’s an issue. This guide will run through five of the most common repairs and the sounds to keep an ear out for.

1. Faulty Blower Motor

If your furnace is making a whistling noise, that usually points to an issue with airflow—specifically the blower. Sometimes it means the blower isn’t getting enough air, whether it’s from a dirty air filter or blocked heating vents. Other times, it points to a problem with the blower motor.

A blower motor can wear out over time, or the bearings can overheat, causing the squealing. It could also rattle if the mount breaks.

How to Fix It

Check your vents to make sure they’re not blocked or closed. Change the filter if it’s dirty. If that doesn’t stop the squealing, lubricating the bearings can help reduce friction and get rid of the noise—but if the bearings are significantly worn, you’ll need to call a pro who can repair your furnace. 

2. Loose Parts

Loose parts are one of the most common causes of a furnace making loud noises. If this is the case, you’ll probably hear your furnace making a rattling or clanking noise. Though this issue can occur with almost any component as it wears over time, the most common culprits are: 

• Fan belts

• Panels

• Ductwork

• Blower wheels

How to Fix It

If you listen, you may be able to pinpoint where the noise is coming from. Check the nearby components for damage or loose fasteners. Tighten loose screws and lubricate the moving parts (the latter will solve any squealing due to friction). If components are damaged, you may need to replace them.

3. Faulty Heat Exchanger

Beyond loose parts, a rattling noise can also point to a faulty heat exchanger. This essential part of your HVAC system transfers the heat created by burning fuel to the air that heats your home using metal coils. Dirty components can stress the heat exchanger, leading to cracks. You’ll hear the noise as soon as the furnace turns on.

How to Fix It

A faulty heat exchanger is serious, because it increases the risk of a carbon monoxide leak. If you hear rattling, you’ll need to repair your furnace ASAP. 

4. Problems with Ignition 

If there’s a problem with your ignition, you’ll hear your furnace making clicking noises as the system struggles to light and start the combustion process. When this process is delayed, a small amount of unburned flammable gas will stay in the combustion chamber. When it eventually lights, you may hear your furnace making a banging noise.

Ignition problems have a number of potential causes. It could be due to: 

• Problems with your pilot light

• Dirty burners

• A broken sensor

• A faulty valve

• A burner malfunction

• Low gas pressure

• A defective ignitor

• A defective control board

How to Fix It

Bring in a pro to figure out the problem. Since this is a gas appliance, you shouldn’t work on the ignition yourself. It can be extremely dangerous. 

That said, some banging noises are normal. You may hear banging if you have metal ducts, which will expand when warm air blows through them. In this case, you can insulate your ducts to stop the noise.

5. Failing Electrical Components

If your furnace is making a buzzing noise or a loudly humming, it may have some electrical issues. This is one of the first signs that a major electrical component in your furnace is failing, whether it’s the blower motor, capacitor, inducer motor, or transformer.

How to Fix It

Faulty or aging electrical components in your gas furnace pose a safety risk, so you should bring in a licensed pro for this repair.

When to Call a Pro

Most of the time, if your furnace is making abnormal sounds, you should call a local furnace repair pro. DIY repairs are especially dangerous when working on a gas appliance because of the risk of a carbon monoxide leak or explosion. Furnaces, in particular, involve complex components, electrical systems, and combustion processes that require specific expertise to handle safely and effectively. 

Although a pro can usually repair a certain component, you may want to consider a full replacement if your furnace is at the end of its lifespan or is an older, inefficient model. A new gas furnace costs $3,800 to $10,000 depending on the specific unit.