My bathroom vent fan vents thru attic about 20 feet to side of house. when fan is turned on, it works fine for about 2 minutes and then starts to rattle loudly. It sounds like the flapper going back and forth but I am not sure. If I disconnect the vent tubing it doesnt make any noise. Thanks

Maybe it's about worn out and as it heats up the motor slows , failing to keep enough air flow thru the pipe to keep the flapper open ?

alot of those units are very simple to replace the 'guts'.
the fan motor has its own plug so no wiring involved.
[toneplusgroup.com]

Thanks for the reply. It is a relatively new unit (3 or 4 years old)

Worn out bearings can cause a rattle, you could try dripping oil on to the bearings and the shaft next to the bearings to see if it helps. When the ducting is disconnected, the load on the motor is reduced.

Impeller blades hitting the housing can also cause a rattle.

Just replace the fan....not too expensive and sleep again.

On some of the ones I've seen there is a vertical flapper valve made of fairly thin metal that opens when the exhaust fan is running, it is pushed out of the way by the moving air, then drops to closed by gravity when the fan is switched off. That thin metal flapper just hangs by a tang in a slot or a small hinge, so it can vibrate due to the moving air and the fan motor vibration.

I'd take a look at the exhaust vent flapper, maybe you can tighten it up somehow. Also look to see if the fan motor mounting screws are loose, causing excessive vibration. If you are not able to quieten it then get a new one.



Edited 2 times.