Hi - Thank you both for your replies.

I am not sure what you mean by ''mechanical'' but, the sound is coming from the transformer itself. It is not too loud but I can hear it from a short distance away. The earth cables are all connected properly. My other 6U case is connected to the exact same power supply and makes no noise - this is what concerned me

--- In Doepfer_a100@yahoogroups.com , Florian Anwander <fanwander@...> wrote:
>
> Hello
>
> I assume you mean a mechanical hum. Right If so, then it should be
> related to the method how the powersupply is fixed to the housing.
>
> Florian
>
>
> On 07.07.13 00:31 , isoldeandisobelle wrote:
> > Hi gang -
> >
> > I have a 6U case and a 9U case, the 9U PSU hums (which changes in frequency when different modules are in use.) - the 6U does not do this.... is this ok
> >
> >
> >
> > ------------------------------------
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
>