weird sub hum

[geoffp]

I have a KEF PSW2500 sub connected to a Denon AVR-2805. Also connected to the receiver (both using optical digital) is DVD player and a media centre PC.

When i first connected the PC, as i didn't have a spare optical cable, I used only analogue L/R connections as a temporary measure. All worked well. When I replaced the analogue cables with the optical cable, the Sub had a very loud rumble/hum.

The weird thing is, i've reconnected the PC and receiver with a single analogue cable, but set the receiver to recognise the digital input and this has removed the hum.

What's causing the hum? I'm presuming it's some kind of earthing problem, but both the PC and receiver are independently earthed, so how does connecting them solve the problem? Any tidier solutions out there?

thanks.
Geoff

[Kimmo Jaskari]

Is there an antenna cable for cable TV or other TV signals involved in this setup? If so, you could have a ground loop between your electrical systems and the antenna.

This can be handled by adding a device to your antenna connector to filter that out (don't ask me where to get one, though... I just know they exist.)