Last January I got a call from a homeowner in Shoreline who said her furnace sounded like “someone dropped a bowling ball in the basement” every time it kicked on. Her husband wanted to replace the whole unit on the spot. Turned out to be a $340 fix. I’ve been doing this since 2017, and furnace noise calls are some of the easiest to diagnose over the phone if you know what to listen for. Let’s go through the seven I hear most, what they usually mean, and what they cost to fix around King and Snohomish counties.
TL;DR
- Banging or booming at startup is almost always delayed ignition, not a cracked heat exchanger, but you still need it checked.
- Squealing points to the blower motor belt or bearings, most jobs run $150-$400.
- Rattling is often loose panels or ductwork, sometimes a $20 fix with a screwdriver.
- Grinding means a motor bearing is failing, and that’s a “replace before it dies in February” situation.
- Clicking that repeats without ignition points to the flame sensor or igniter, common in furnaces 10+ years old.
- If your furnace is past 15 years old and needs a $900+ repair, I’ll usually tell you to price out replacement or a heat pump installation instead.
- Call (206) 427-8907 if you’re not sure which noise you’re hearing, we can usually narrow it down before we drive out.
The Loud Bang or Boom at Startup
This is the one that scares people the most, and I get it. It sounds like something exploded. Nine times out of ten, it’s delayed ignition. Gas builds up in the burner chamber for a second or two longer than it should, then lights all at once instead of smoothly.
Causes I see most in older homes around Lake City and Ballard: dirty burners, a cracked or misaligned igniter, or low gas pressure. Cleaning the burners runs about $150-$250. If the igniter needs replacing, add another $120-$180 in parts and labor.
Here’s the part I don’t sugarcoat: delayed ignition stresses the heat exchanger over time. One or two bangs won’t crack it, but months of it will. If your furnace is banging every cycle, don’t wait through a whole heating season to deal with it. That’s how a $200 repair turns into a $3,500 heat exchanger replacement, and at that point I’m telling most homeowners to look at a new system instead.
“Callers describe noises better than they think: ‘jet engine on takeoff’ is almost always airflow or blower, ‘coin in a dryer’ is something loose, and the boom on ignition gets my urgent slot every time. Record ten seconds on your phone before calling — it genuinely speeds up the diagnosis.”
— Alina Kovalenko, Service Coordinator & Comfort Advisor at SPS Pro Services
Squealing or Screeching When It Runs
This is belt or bearing noise, almost always in the blower motor. Older furnaces (pre-2010ish) still use belt-driven blowers, and belts stretch or crack. Newer direct-drive units skip the belt, but the motor bearings can still squeal as they wear out.
A belt replacement is a $150-$250 job. Bearing issues in a direct-drive motor mean the whole motor gets swapped, which runs $350-$550 depending on the furnace brand. I had a Bellevue customer whose furnace ran fine except for this screech every startup for six months. By the time she called, the motor had seized and took out a capacitor with it. What would’ve been a $180 fix became a $420 one. Squealing doesn’t fix itself.
Rattling Panels and Ductwork
This is the good news noise. Rattling is usually loose sheet metal, either a furnace access panel that isn’t seated right or ductwork that’s expanding and contracting as it heats up. I check the panel screws first on every service call, because it takes thirty seconds and solves maybe one in five noise complaints for free.
If it’s the ducts themselves, especially in older homes in Everett with original 1960s-70s ductwork, we sometimes add support straps or foam padding where the duct touches a joist. That’s usually under $150 in labor.
Grinding or Metal-on-Metal Scraping
Grinding is a bearing that has already failed, past the point of plain wear. Metal is contacting metal. This is the noise where I tell people to shut the furnace off and call us that day, not next week. Running a furnace with a grinding motor can cause it to seize mid-cycle, sometimes with a burning smell, sometimes tripping a breaker.
Replacement blower motors run $350-$600 installed depending on furnace age and whether the part is still stocked by the manufacturer. If your furnace is 14+ years old and the motor’s shot, I usually walk homeowners through the math on repair versus replacement, because a new blower motor on a dying furnace is money you won’t get back.
Repeated Clicking Without Ignition
If you hear click-click-click and the furnace never actually lights, that’s a flame sensor or igniter problem, not a noise problem exactly, but it’s the complaint I get. The sensor gets a thin layer of carbon buildup over a season or two and stops reading the flame properly, so the control board shuts gas off as a safety measure and tries again.
Cleaning a flame sensor is a $90-$130 service call in most cases. If the igniter itself is cracked, that’s a $120-$200 part and labor job. This is genuinely one of the cheapest furnace fixes there is, so if a company quotes you more than $250 for a flame sensor cleaning, get a second opinion.
Humming or Buzzing With No Airflow
Humming with no air moving usually means the blower motor is trying to start but can’t, often because a capacitor has weakened. Capacitors are cheap parts, $20-$40, but labor to diagnose and swap runs the total to $150-$220. This is a very common call in July when AC repair season overlaps with people testing their systems, since the blower motor and capacitor are shared components in a lot of combo systems.
Whistling Around Vents or Return Air
This one’s usually not the furnace at all, it’s airflow restriction. A dirty filter, a closed vent, or a return air grille that’s too small for the system. I’ve walked into three houses in Seattle this year where the “furnace noise” was just a filter so clogged the system was straining to pull air through it. Swap the filter, problem gone, zero dollars if you had a spare.
Furnace Noise Repair Cost Comparison
| Noise | Likely Cause | Typical Repair Cost (Seattle area) | Worth Fixing If Furnace Is… |
|---|---|---|---|
| Bang/boom at startup | Delayed ignition, dirty burners | $150-$250 | Under 15 years old |
| Squealing | Belt or motor bearings | $150-$550 | Under 15 years old |
| Rattling | Loose panel or ductwork | $0-$150 | Any age |
| Grinding | Failed motor bearing | $350-$600 | Under 12 years old |
| Repeated clicking | Flame sensor or igniter | $90-$200 | Any age |
| Humming, no airflow | Weak capacitor | $150-$220 | Under 15 years old |
| Whistling at vents | Dirty filter or blocked return | $0-$50 | Any age |
These numbers are estimates based on typical service calls in King and Snohomish counties. Your actual cost depends on furnace brand, part availability, and access.
Quick Checklist Before You Call
- Replace the filter if it’s been more than 90 days, this fixes whistling and some humming complaints outright.
- Check that the furnace access panel is fully seated and screwed in.
- Note when the noise happens: at startup, mid-cycle, or shutdown. This tells us a lot before we even arrive.
- Check your thermostat batteries if you’re getting short-cycling along with clicking.
- If you smell gas or burning along with the noise, shut the system off and call us immediately, don’t wait for a scheduled appointment.
- Write down the furnace’s age and brand if you know it. It’s on a sticker inside the front panel.
When Repair Isn’t Worth It
I’ll say this plainly because a lot of contractors won’t: if your furnace is 16+ years old and needs a repair over $700, get a replacement quote before you approve the fix. I’ve seen homeowners in Everett and Bellevue sink $600 into a 17-year-old furnace in November, then have it fail completely by February anyway. Furnaces have a working life, typically 15-20 years with regular maintenance, and once you’re near the end of that window, every repair is a bet against the calendar.
This is also a good time to think about whether a furnace repair even makes sense versus switching to a heat pump, especially if your home doesn’t have central AC yet. A lot of our Seattle and Bellevue customers are making that switch specifically because it solves heating and cooling with one system. If your electrical panel is older or under 100 amps, that’s worth checking too, since heat pumps and things like an EV charger installation or future electrical panel upgrade sometimes go hand in hand with a heating system replacement.
Mini FAQ
Is a loud furnace dangerous? Not automatically, but grinding, banging, or any noise paired with a burning smell means shut it off and call someone. Rattling and whistling are almost never safety issues.
Can I fix furnace noise myself? Filter changes and tightening an access panel, yes. Anything involving the blower motor, ignition system, or gas components should go to a licensed tech, both for safety and because opening those parts yourself can void what’s left of a manufacturer warranty.
How often should I get my furnace serviced to avoid these noises? Once a year, ideally in early fall before the first cold snap. Most of the noise complaints I run into trace back to a furnace that hasn’t been serviced in two or three years.
If your furnace is making a noise you can’t explain, call us at (206) 427-8907 and we’ll help you figure out whether it’s a $90 fix or something bigger before we ever set foot in your basement.