Furnace Making Noise? Here’s Why

December 14, 2021
Furnace Repair in Seattle, WA

Is your furnace squeaking, clanging, and banging? Unusual sounds are a sure sign that something’s amiss with your heating system. The team at Brennan Heating & Air Conditioning has dealt with every sound a furnace can make, and we have professional furnace repair solutions for all of them. However, to the untrained ear, it can be difficult to tell what’s wrong with the unit. We put together this helpful reference article to help you answer the burning question, “why is my furnace making that sound?” Our Seattle furnace technicians are here to help you understand what’s wrong with your furnace and are standing by to make quality repairs.

Before we dive into what causes furnace sounds, let’s take a look at the most common sounds furnaces make. The specific sound your furnace makes is important because it can clue you in to the underlying issue.


Clicking is most often heard when the furnace is starting a new cycle. Usually, you hear this just once every 10-15 minutes when each new cycle begins. If you hear the click more often, that means your furnace is doing something we refer to in the industry as “short cycling.” A short cycle is when something is preventing your furnace from completing a full 15-minute heating cycle. This could be due to an issue with the control board, a burned-out ignitor, or a loose internal component.


Rattling is another common noise that furnaces make when something has gone awry. The most common culprit is the blower motor. If the motor becomes loose or dirt gets stuck under the wheels, it will create a noticeable rattling sound. In addition to the blower motor, loose components like screws or scrap metal can also make the system sound like it’s rattling.


Furnace components undergo a ton of wear and tear throughout the year. As pieces start to wear out, they may begin making a squeaking or squealing sound when the heater is running. Usually, the culprit is a small metal component, like the induction motor or blower bearings. Regardless of the exact cause, the sound of metal scraping against metal is never a good sign and should always be subject to professional troubleshooting.

Now that we’ve explored the different sounds your furnace can make, we’re ready to look at the most common causes of unusual furnace sounds.

Dirty Burners

Loud sounds like bangs and booms are characteristic of a dirty burner. The burner is a furnace component that ignites fuel to generate heat. If the burner gets dirty, it will cause a delay in the ignition, which allows gas to build up. Instead of igniting immediately, the slow ignition causes a larger gas explosion than normal, creating a loud boom. While this issue isn’t normally dangerous, it’s still best to have it repaired, so it doesn’t worsen. Routine maintenance can also prevent this issue from happening in the first place since the tune-up includes cleaning the burner.

Air Leak

A high-pitched whistling sound reminiscent of a tea kettle is usually a sign of an air leak. These pesky leaks usually pop up in the air duct system. At the ducts age, their seams can deteriorate and let out tiny amounts of air. The result is a telltale whistling sound accompanied by a spike in utility costs. Air leaks usually start out minor but can become detrimental over time since they reduce your HVAC system’s energy efficiency and cause it to work harder. Luckily, leaky ducts are usually easy to repair and can be caught during annual maintenance appointments. If your ductwork is very old, your technician will also discuss the possibility of duct replacement.

Damaged Blower Wheel

A damaged blower wheel is one of the most well-recognized furnace issues because it creates a terrible racket. The first thing you’ll notice is a loud, screeching sound like metal scraping on metal. As soon as you hear this sound, you should turn off the furnace. Allowing the furnace to continue running can cause serious damage to the system, resulting in pricey repairs or even a full replacement. If you hear this sound, call us right away, and we’ll have the blower wheel replaced with speed and professionalism.

Unbalanced Blower Wheel

The blower wheel doesn’t necessarily have to be damaged for it to cause trouble. Even an unbalanced furnace blower wheel can be problematic. This issue is often caused by a foreign object, like a piece of paper or ball of pet hair getting trapped near the blower wheel. In other cases, a faulty balancing weight can cause the same problem. This creates a sound similar to an unbalanced washing machine. Left untreated, an unbalanced motor wheel can cause damage to other parts of the HVAC system, so it should be investigated and repaired right away.

Blower Motor Bearings

High-pitched whining and squealing can indicate the bearings in your furnace’s blower motor are worn out. Bearings can have a long lifespan–up to 30 years–with the proper maintenance routine. However, these bearings can wear out prematurely if the furnace is overheating. Furnaces overheat for a variety of reasons, from bad capacitors to clogged air filters. For these reasons, it’s essential to have your furnace professionally inspected at least once per year. It’s also critical to keep up with at-home maintenance steps like replacing the air filter every three to six months.

Cracked Heat Exchanger

Does your furnace click when it’s running? Furnaces often click when the heat exchanger is cracked. Since heat exchangers are made of metal, they naturally expand and contract as the temperature in your furnace rises and falls. Although the heat exchanger is sturdily designed to adapt to these changes, years of wear and tear can cause the component to fracture. As the exchanger continues to expand, the fracture gradually worsens, and the noise becomes louder.

Although a crack may not sound so bad, cracked heat exchangers are actually the leading cause of residential carbon monoxide poisoning. Carbon monoxide is a dangerous and sometimes lethal gas, so if you hear your furnace clicking, be sure to have it examined by a professional ASAP! Brennan Heating & Air Conditioning offers 24/7 emergency furnace repairs for situations just like this one.

Loud Transformer

A humming furnace could be a sign of a bad transformer. Although healthy transformers naturally hum, they should be relatively quiet. In other words, hearing a hum when you’re standing next to the furnace isn’t necessarily a problem, but hearing it in the next room is almost certainly a sign that repairs are needed. A faulty transformer isn’t usually grounds for an emergency, so you can probably allow the heater to continue running until our technician arrives. When you call in and fill us in on the details, we’ll let you know if there are any special precautions you should take before we arrive.

Expert Furnace Repair in Seattle

Knowing why your furnace is making a strange sound is the first step towards troubleshooting the problem and finding a solution. While some issues can be diagnosed at home, it’s always best to have the system looked over by a trained professional. Here at Brennan Heating & Air Conditioning, we have more than 30 years of experience inspecting, diagnosing, and repairing furnaces all over Seattle and Puget Sound. No matter what’s wrong with the furnace, we’re confident we’ll get to the bottom of it and fully restore your furnace to peak condition.

Brennan Heating & Air Conditioning is a leading provider of heating and air solutions throughout Seattle. We’re happy to provide repairs, installations, maintenance, and replacements. We also provide water heater service and residential electrical solutions. Throughout our many years in business, we’ve earned a reputation for being prompt, professional, and honest. That’s why we earned the Angie’s List Super Service Award Winner for 13 years in a row and an A+ rating from the Better Business Bureau. When you partner with us for your home heating and cooling needs, you can look forward to working with a down-to-earth contractor dedicated to earning your complete satisfaction.

To schedule furnace service, call us or reach out online today!

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