Any tricks for silencing a Hella Turbo cabin fan???

[tudorsailor]

I have Hella turbo fans in the cabins and the galley. Some are quiet whatever position they are in but others are REALLY noisy in most positions and one needs to play to find the one position in which the blades are not knocking. This usually is the least desirable position of air flow of course
Are there any tricks to making the fans quiet in all attitudes??
Thanks from sweaty Greece!
TudorSailor

 

[PotatoNavigator]

Turn it off?

 

[sailorman]

Is he taking the pith