Loud, grinding, or screeching noise during operation
If your oven, hood, warmer, proofer, walk-in condenser, or any other commercial unit sounds like it’s chewing gravel — that’s not “normal for its age.” Loud mechanical noise is a warning.
The two sounds I pay the most attention to are:
- Grinding / rattling / metal-on-metal
- High-pitched squeal / screaming fan / whistle under load
Those usually mean one thing: something that spins is failing.
Let’s go through:
- where that noise is coming from,
- what it’s telling you,
- when it’s just annoying vs when you should shut it down,
- and what we actually replace or tighten to get it quiet and safe again.
What the kitchen usually tells me
I’ve heard all versions of this:
- “There’s a horrible grinding noise when it runs.”
- “The fan sounds like it’s about to explode.”
- “It used to hum, now it screams.”
- “We hear a buzzing / rattling from the back wall whenever it’s on.”
- “It starts quiet and then gets LOUD once it heats up.”
If your crew is stepping away from the unit because they don’t trust it, listen to them. They’re usually right.
The #1 source of nasty noise: fan assemblies
Most commercial hot equipment — ovens, holding cabinets, combis, proofers, even some fryers and undercounter refrigeration — relies on one or more fans.
Different fans do different jobs:
- Convection fan / circulation fan: moves hot air evenly through the cavity.
- Cooling fan: keeps control boards, wiring, transformers, and other electronics from cooking.
- Exhaust or vent fan: moves air out of the unit or keeps vapors down.
- Condensing fan (refrigeration): moves air across coils in cooling equipment.
When one of these fans starts failing, you hear it.
Here’s how.
Noise type: Grinding / scraping / rattling
That “metal dragging on metal” sound? That’s usually mechanical contact.
Common causes:
- Fan blade hitting something
- Blade is bent.
- Blade is loose on the shaft and wobbling.
- A screw, wire, or piece of debris is physically touching the blade as it spins.
- Fan shaft is loose in the bearing
- The motor bearings are worn out.
- The fan wobbles off-center while it runs.
- The whole assembly vibrates against its housing.
- Mounts are loose
- The fan or motor was mounted with screws/brackets.
- Over time (heat, vibration), those fasteners back out.
- Now the entire motor is shaking the panel it’s bolted to like a drum.
Why this matters: when a fan blade hits metal, it can shatter, throw pieces, or damage the heating element / wiring in that area. I’ve seen fan blades carve through insulation and start electrical shorts. This is not just “annoying noise.”
What we do in this situation:
- Kill power, open the panel, and inspect the fan assembly.
- Check the blade for damage, warping, buildup throwing it off balance.
- Check that the motor is actually tight on its mount and not about to fall out.
- Replace a bent fan blade or failed motor.
- Secure and re-torque mounts so it can’t vibrate itself apart again.
If the fan is physically striking something, that unit should not stay in service like that. That’s how you end up with parts in food, wiring damage, or complete fan failure mid-rush.
Noise type: High-pitched squeal / squeaking / screeching
That screaming, nails-on-glass pitch? That’s almost always bearings.
Fans use bearings to let the shaft spin smoothly. Over time:
- Heat dries them out.
- Grease/steam/oil gets in and gums them up.
- The bearing starts to seize.
When a bearing is going:
- You get chirping or squeal on startup.
- You get a “police siren” type wail once the fan is hot.
- Sometimes the noise changes when you open/close the door or when the unit cycles power.
What that noise is telling you is:
“I’m about to lock up.”
When a cooling fan or convection fan locks up, two bad things happen:
- You lose airflow.
Now you’re not moving hot air where it should go. - You overheat something else.
- If it’s a convection fan: the oven cooks unevenly, overheats one spot, and might trip high-limit and shut down.
- If it’s a control cooling fan: the control board or wiring cooks, and you’ll start blowing components.
What we do in this situation:
- Check the fan motor for bearing play and drag.
- Listen for pitch changes when we spin it by hand.
- Replace the motor (in most commercial gear, you don’t “lube it and send it back,” you replace it).
- Confirm the fan spins freely and quietly after install.
If you’re hearing squeal, it’s a “fix soon” problem. If it stops squealing and goes quiet suddenly, that’s usually because it stopped spinning at all — which is worse.
Noise type: Low, heavy vibration / buzzing panel
This one sounds like the whole unit is humming or buzzing against itself. Sometimes you even feel it through the stainless.
Common causes:
- A blower or fan is out of balance from grease buildup on the blades.
- The motor mount is loose and the motor is basically shaking the frame.
- One of the mounting brackets or internal panels cracked or backed off a screw, so now it’s acting like a resonator.
It may not sound “sharp” or “scary,” but this kind of vibration can:
- Shake wiring loose.
- Crack solder joints on control boards.
- Fatigue fan blades and send them flying later.
- Walk screws out until something drops inside the unit.
We usually pull panels, tighten and/or re-secure mounts, clean the fan blades, and replace anything that’s bent or cracked so the assembly sits solid again.
Noise that starts quiet and gets bad after it heats up
This is really common and super important.
If the unit is quiet when cold but starts screaming / grinding / rattling after 5-10 minutes at temp, that’s thermal expansion telling on a failing part:
- Heat is causing a warped fan blade to start hitting the housing.
- Heat is causing already-dry bearings to seize under load.
- Heat is causing a loose mount to flex until it buzzes.
In other words, “it’s fine when we first turn it on” does not mean “it’s fine.”
It means “it’s about to fail under real conditions.”
We test under real temperature, not just cold idle, so we can catch that.
When is loud noise just annoying, and when is it dangerous?
You should take the unit out of service now and call for service if:
- The noise is metallic grinding (blade-on-housing).
- You can smell hot wiring, hot dust, or a “burning motor” smell.
- The noise is paired with performance problems (overheating, shutting off mid-cycle, poor airflow, uneven cooking).
- The unit physically vibrates or walks across the table / floor.
- You see the fan visibly wobbling or sparking.
That’s not an “after lunch” situation. That’s “turn it off before it takes itself — and maybe something else — out.”
If it’s just a mild hum but everything is stable, temperatures are good, and nothing’s overheating, it’s still worth checking soon. Noise almost never gets better on its own.
What we do on a service call for “it’s making noise”
Here’s our normal flow:
- We listen to it under real load.
We don’t just flip it on for 5 seconds cold. We run it hot, how you actually use it, because some failures only show up at temp. - We isolate where it’s coming from.
Is the sound coming from:- the cavity fan,
- the control/cooling fan,
- the hood/exhaust section,
- the condenser section in the back,
- or a loose panel?
- We inspect the fan blade and mount.
We check for bent blades, missing screws, cracked housings, loose brackets, and grease buildup that’s throwing the rotor off balance. - We spin-test and bearing-test the motor.
We check for wobble, scraping, heat in the motor housing, excessive resistance, and that classic “dry bearing squeal.” - We replace what’s failing.
Typical fixes:- New fan motor (cooling or convection)
- New fan blade / impeller
- Tightening or replacing mounts and brackets
- Cleaning and rebalancing a blower so it doesn’t vibrate the whole cabinet
- We run it again.
Quiet, steady airflow, no rubbing, no rattling, stable temps. If I can stand next to it and talk at a normal voice, we’re good.
FAQ: Loud / grinding / squealing equipment
Why is there a grinding noise when the oven is running?
Most likely the convection fan or cooling fan is rubbing, bent, or loose. That’s usually mechanical contact — blade hitting housing or a motor bearing failing.
The fan is screaming like a jet engine when it heats up. Is that normal?
No. That high-pitched squeal is usually a dying bearing. That fan can seize, and if it’s a cooling or circulation fan, that can lead to overheating and shutdown.
Can I keep using it if it’s noisy but still “works”?
Short-term maybe, but you’re gambling. A failed fan can cascade into overheating, high-limit trips, cooked control boards, or metal fragments. It’s cheaper to fix the fan than replace the whole section after it takes itself out.
Can you just tighten it?
Sometimes, yes — if the issue is loose mounting hardware. But if the bearing is shot or the fan blade is deformed, we replace parts. Tightening won’t fix internal wear.
Why does it only make noise after 10 minutes, not right at startup?
Because heat changes clearances. Once metal expands and bearings get hot, the failing part starts rubbing or locking up. That’s an early warning for “about to die under load.”
Final word from a tech
Loud grinding, rattling, or squealing isn’t “annoying background noise.” It’s the machine telling you:
“I’m shaking myself apart,” or “My fan is about to seize,” or “I’m overheating internally.”
What we do:
- Find the noisy fan (convection, cooling, exhaust, condenser, etc.).
- Replace the bad motor or blade.
- Re-secure the mounts so the assembly can’t rattle itself to death.
- Test it hot to make sure it runs quiet and moves air the way it’s supposed to.
End result: no screaming bearings, no metal-on-metal grinding, no mystery rattle behind the line — and way less risk of the unit cooking itself or dying in the middle of service.