What’s Causing These Furnace Noises?

When furnace noises start, there can be a lot of questions. We’ve created a short list of common sounds that we have accumulated from decades of combined experience in the HVAC field serving Central Maryland. Our technicians are highly skilled, trained, and experienced, and our Diagnostic equipment is state of the art to bring you precise solutions for all of your furnace repair needs. We are ready to remedy all these noises, safely, often saving your money!

Can I Fix Furnace Noises Myself?

Well, you should consult a professional HVAC technician who can come to your home or business to see, hear, smell, and diagnose your actual furnace issue. This article is in no way a comprehensive or accurate answer to your specific furnace noises or issues, but is an interesting compilation. It is UNSAFE, and dangerous to work on your unit without proper training. Call a professional HVAC company for everyone’s safety.

What Furnace Noises Are OK?

Before we discuss problematic sounds, let’s review some normal noises a furnace makes which are rarely cause for concern:

  • Chirping from your furnace likely is just natural noise from its mechanisms.
  • Rattling noises that occur as the system cools down from a cooling cycle are generally ok.
  • Crackling once a heating cycle ends is usually caused as metal components cool.
  • Pinging sounds may also result from metal contracting in the duct system.
  • A faint hum and a slight click typically occur when the burners ignite – this is normal.

Problematic Furnace Noises

The furnace noises you need to watch out for include:

  • Scraping or screeching metal
  • Grinding
  • Flapping sound
  • Buzzing, humming, or rattling
  • Pops or bands at startup
  • High-pitched squeaking or squealing
  • Duct sounds

Metallic scraping or screeching as furnace runs

This is likely the blower wheel, and will not get better over time if left alone. In most cases, if left untreated, the wearing will produce metal shavings or filings which will fall onto, and into other parts. With their tiny size, they can easily work their way into the smallest openings and damage electrical boards, wiring, and moving parts.  

When these are steel shavings (attracted by the magnets in the electric motor), they can hamper effectiveness and eventually cause failure. Catching this early is simple, and waiting will be more costly and inconvenient to you.

Grinding while furnace runs

This likely means the blower bearings are worn to the point of no return. It is likely in older furnaces that time has simply worn the bearings; on newer units, it can be that the belt tension has stressed the system.  

Call as soon as possible, as this can be dangerous, and catching it early can mean savings! Letting the problem continue can affect other furnace components, and cause more costly failures.

Flapping sound when furnace cycles

This can be serious, but also can be as simple as an object getting sucked in through the air intake which has become stuck in several possible places. The item has to be small enough to get in through the vent – like a piece of paper, yet large enough to get stuck in the system.

Solving this means entering the furnace system. It should be solved when noticed and often these furnace noises can be remedied during a fall maintenance request.

Buzzing, humming, or rattling

This can be something as simple as a loose mounting screw or loose door. This could also be a partially installed furnace filter. Take a look at these areas in the location of the vibrating noise. If not solved with a simple loose door cover or screw, this issue needs to be found, and solved by a professional soon to prevent further damage.

Pops or bangs when furnace starts

This is often a “dirty” igniter/burner. When the igniter starts to become clogged, the initial gas is not lit and there is a buildup of gas before the weak igniter can start to light it. With the excess gas buildup and eventual ignition, the larger amount of gas will make the “pop”, or if large enough, a “Bang” as the larger mass of gas ignites.  

This is an important time to call since these are obviously dangerous issues. They are able to easily damage the surrounding components if not fixed quickly, including costly pieces like the furnace’s heat exchanger.

Squeak, whine, or squeal at startup

Often this is loose or worn belts, however, it may be the motor shaft, bearings, or the motor itself. You may be familiar with this type of noise coming from a car or truck with a bad belt. Your furnace belt can experience the same condition.  

Fixing this can be very affordable but is best done by a professional because the proper tension is best done by experience. Over and under tensioning creates damage to the motor, and any or all of the components which the belt is driving noises from the furnace.

Sounds from ducts

Low bass sounds of popping, thumping, or bonging are typically expanding or contracting vents and duct work. This is common when the design and installation has undersized ducts, loose vents or ductwork, failing joints, or the ducts are touching other parts of the home structure. When heat expands, the ductwork metal pops back into its cooler, contracted state.  

If this is the true root cause of the sounds, it is rarely damaging, but can be annoying, and even disturb sleep. If you are hearing these noises, even from ductwork in a new or increasing volume, it would be best to get it checked by a professional.  Your fall HVAC maintenance appointment is a great time to inspect these sounds!

Fix Furnace Noises with Grove!

Whatever the noise, sight, smell or concern, we at Grove Heating and Cooling are ready to help with all your HVAC, heating system, and furnace needs for all of Central Maryland. Contact us now if you need furnace repair! Our 24-hour emergency furnace repair and replacement service has been refined and improved with our decades of combined experience to bring you superior HVAC services 24/7/365, starting with a live person on the phone, and finishing with our HVAC industry leading certifications, guarantees, and manufacturer’s warranties.