Do not need it, since your ears are picking up the echos, which are amplifying the fan when it is running, if the door is closed. If you whisper in the bathroom, you would be surprised how much louder it sounds, then in another room.Broan XB 110 fan is what we were told was good. specs say <.3sones.
I have a sound file of the loud noise. but do not see how to post it!