Re: Retrofit Bath Fan
Nearly all of the noise of an exhaust fan is caused by the movement of air; the motor itself is pretty quiet. If something's unbalanced, that can create vibration.
Vibration can sometimes be dampened by using bits of rubber tape or foam between the "guts" and the outer case.
Most of the noise comes from the blower wheel; you might be able to upgrade just that part.
If the exhaust duct is flexible, you may be able to replace the entire unit from below. (In the process you'll end up destroying it.) Use brute force to push the existing housing up into the attic, giving you space to disconnect it from the exhaust duct, wiring, and framing. If brute force doesn't work, use more. Purchase a new unit that is the same size or larger than the existing hole, and designed for "old work" installation. The hard part will be replacing the insulation that is currently covering the existing fan.
The quietest exhaust fans are designed considering the whole system: the intake screen, blower, case, motor, and exhaust damper are all engineered to reduce turbulence and move air quietly.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.