reduce ventilation fan noise
 

Due to lack ceiling space of my bathroom, I can not install those low noise type of ventilation fan, so I have installed 3 sones ventilation fan on interior wall of bathroom, but the noise is quite loud especially night time.

My questions
1. Is any low noise inner wall mount ventilation I can buy?
2. Can I modify that fan to low noise DC type fan?

Thanks

If this is a ceiling mount fan that you decided to mount on a wall instead it's never going to work out, The bushings or bearing inside of it were not ment to be side loaded.
They make wall mount exhost fans but your going to have to run 110 volt wiring to it.

The smaller the pipe the more the noise, you probably have 3" pipe in the wall and the fan is chopping the air.