Some Noise is Expected
All bathroom fans make noise, but some create such a disturbance that owners avoid using them. This is especially bothersome in a guest bath or powder room. I get many calls as a handyman for this one issue. It appears the problem is that builders generally install the cheapest model fan available when installing a bathroom, and cheap fans are noisy fans. While there is little that can be done, short of replacing it with a new fan, to stop the noise altogether, there are some things that will lessen the noise.
How to Inspect
The first step is to turn off the circuit breaker or remove the fuse that controls the fan; if the breaker isn’t labeled, just turn on the fan and switch off breakers until it stops. Then, remove the fan cover. Most fans have (2) wire clips that hold the cover in place. Just pull on the cover and it should slide down about 3” from the ceiling. Once the cover is loose, look inside to determine what will be required to remove it completely. In most cases you’ll squeeze the wire clips on each side and pull them from their anchor slots.
Once the cover is removed, turn the breaker and fan on and observe its operation. You’ll probably find the fan covered with a thick layer of dust, which should be vacuumed away before continuing (turn off the power for this step). Many older models had metal fan blades that, if slightly bent, will make contact with the housing. If that is the case, the metal blades are easily straightened by pressing slightly with a screwdriver or your finger. If cleaning or adjusting the blade fails to fix your problem, you may be able to replace the fan mechanism only—many models are interchangeable and replacement is simple.
Replace the Motor/Fan
First, unplug the electrical cord from its receptacle and then slide a flat screwdriver between the fan housing and the metal bracket that supports the fan mechanism. The fan motor assembly should be relatively easy to remove. Once removed, take it to your local home center and see if you can match it to a new one. There are replacements for some models, and if you are lucky enough to find one, it’s a simple matter to pop it in the old housing, and you’ll soon be rid of the noise problem. There is a good step by step instruction page here.