Hi Pierre

> Quick question: do your PSUs make an audible buzz/hum

Yes it does. It is - as the others said - a mechanical hum from the
transformer. If you have a standard power supplies mounted to the rear
side of the rack, the hum will be louder than from a modul like power
supply, because the back plate of the housing works as resonator.

To me this hum is quite annoying, because I always have to switch off
the modular when I do microphone recordings - and now guess where the
powerswitch is located and how reachable it is...

A solution might be to mount the powersupply on a foamed rubber plate
and mount this rubber plate to the housing.

Florian