Why Your Furnace is Making Noise – 6 Reasons and How to Fix Them

Air conditioning systems and heating systems can both make sounds no matter if they are on or off, so it’s normal to hear strange furnace noises once in a while. 

However, the best way to determine why these loud noises are happening is to first understand what they sound like and what issues they could be hinting.

A Banging Noise

• Banging noises or popping sounds in your furnace are usually caused by a small gas explosion following a delay in ignition. The gas basically builds up in the combustion chamber and creates a clogging or gas pressure problem. 
• These noises are pretty common because the ducts expand and contract, but if you think they are louder than before, they could potentially point to an issue with your furnace.
• The Solution: If in doubt, call a licensed technician. Do not attempt to disassemble the heat exchanger or burner, or you could cause a gas leak and compromise your safety. 

A Whistling Sound

• If your furnace makes a whistling noise, this might mean there is a clogged air filter that is causing the airflow to become restricted. The blower can also develop low airflow issues and result in a high-pitch sound.
• The Solution: Consider changing your furnace’s air filter and see if the whistling sound disappears. If the fix is ineffective, call a technician for additional assistance. 

A Popping Noise

• A popping noise can be a sign of inflation in your furnace’s air ducts – especially if you hear this sound right after you turn on the system. 
• What usually happens is that the warm air reaches the cold air ducts, and the metal enlarges to accommodate the temperature change. Another reason for popping noises can be contaminated gas burners (or an accumulation of sediment and debris).
• The Solution: Ask a certified technician to inspect your ducts or remove the debris causing the sound before it causes holes in your heat exchanger. 

A Screeching or Squealing Noise

• These types of noises are usually due to issues with the blower motor, which has bearings that tend to wear over time. Another possibility is a broken belt.
• The Solution: Luckily, if the screeching and squealing sounds are coming from the motor, they can be fixed with some lubricant. You can choose to apply mineral or synthetic oil yourself or call a professional to do it for you. A technician will also be able to replace your furnace’s belt. 

A Rattling Sound

• Rattling rumbling sounds frequently indicate that something has come loose inside your furnace. This causes a vibration that can also result in other components breaking.
• The Solution: Hire a certified technician to inspect the blower motor, the heat exchanger, the gas burners, and the hot surface ignitor. They will have the tools necessary to tighten any loose furnace parts. 

A Scraping Noise

• Scraping sounds are usually caused by worn-out ball bearings. Another possibility is that the blower wheel has come loose. Although this sound can be quite alarming (the sound is that of metal rubbing against metal), it can usually be fixed with a simple part replacement.
• The Solution: Turn the furnace off immediately to prevent wear and tear, and call a certified HVAC professional.