By the WY&G, Inc. team: licensed HVAC contractor, CSLB C-20 #1044922, over 25 years and thousands of customers in the Santa Clarita Valley and Orange County.
Normal furnace sounds
- A click or two when the thermostat calls for heat
- The hum of the small inducer fan starting
- A soft whoosh as the burners light
- Light ticking or popping from metal ducts as they warm and cool
- The steady sound of air moving once the blower starts
If your furnace has always sounded like this, there's nothing to fix.
Banging or booming at startup
A single loud boom right when the burners light is usually delayed ignition. Gas builds up for a moment before it lights, then it all lights at once. Causes include dirty burners, a weak igniter, or gas pressure that's off. It's more than a noise problem. Over time those small explosions stress the heat exchanger, so turn the furnace off and have it checked.
A softer bang or pop from the ducts, a few seconds after the blower starts, is different. That's sheet metal flexing as air pressure changes. It's often a duct or return issue rather than a safety one, but it's still worth mentioning on your next visit.
Squealing or screeching
- Blower motor bearings wearing out. The squeal often starts when the fan comes on.
- Inducer motor bearings. A high pitch whine right at startup, before the burners light.
- A worn or loose belt on older belt drive furnaces.
A motor that squeals today can seize later, usually on the coldest night. Get it looked at before then.
Rattling
- A loose access panel. The easiest one. Make sure the furnace door is seated and latched.
- Loose screws on the cabinet or a duct connection.
- Blower wheel loose on its shaft, or debris inside it.
- Inducer wheel starting to fail.
In rare cases a rattle comes from a cracked heat exchanger expanding as it heats. That's one more reason a new rattle deserves a look.
Humming, buzzing, clicking, whistling
- Loud hum or buzz: often a failing capacitor, a transformer, or a motor trying to start and not able to.
- Repeated clicking with no flame: the ignition is trying and failing. See ignition and flame sensor repair.
- Whistling: the system is starved for air. Check for a clogged or wrong size filter, closed vents, or a blocked return grille.
Noises from the ducts and vents
Not every sound comes from the furnace itself. A whoosh or roar at the return grille usually means the return is too small for the blower, which is common in older homes with a single return. Rattling at a vent cover is often just a loose register screw. A boom from the ductwork when the fan starts or stops is sheet metal flexing, and it tends to get worse with a dirty filter or closed vents. These are worth fixing for comfort, but they aren't emergencies.
Why an old furnace gets louder
Bearings wear, mounts harden, and panels that were snug for years start to buzz. A furnace that's been running in a hot Santa Clarita attic for many summers ages faster than one in a mild closet. A new sound is information. Catching it while it's just a sound usually means a smaller repair than waiting until the motor stops.
Grinding or scraping: turn it off
Metal on metal grinding usually means a motor bearing is failing or the blower wheel is rubbing the housing. Running it can burn out the motor. Switch the furnace off at the thermostat and the service switch, and call.
What you can safely check
- Replace the air filter with the correct size.
- Open supply vents and clear the return grilles.
- Press on the furnace door to make sure it's latched.
- Note when the noise happens: at startup, when the blower starts, while running, or at shutdown. That timing helps the technician a lot.
Leave motors, burners and the gas valve to a technician. If the furnace is old and noisy and needs a big part, our article on furnace repair or replacement may help.
Noisy furnace repair near you
WY&G is a licensed HVAC contractor (CSLB C-20 #1044922) with over 25 years in the Santa Clarita Valley and the north San Fernando Valley. Most repairs happen the same day. See furnace repair, or our pages for Valencia, Granada Hills and Porter Ranch. Call (323) 240-2373 or book online. Code WEB25 takes $25 off (coupons).
