PC Digital Audio studio noise problem

Archived from groups: rec.audio.pro (More info?)

Hi all. I hope someone can help.
I have a PC digital audio setup with a Yamaha S80, a mixer, a PC.
The S80 plugs into a Behringer MK 602A mixer which in turn plugs into the PC
sound card - Terratec EWX 24/96.
I am picking up digital noise and a clock ticking sound from the S80 audio
outputs, even when the power switch is off. It's faint but it can be
detected on headphones. I unplug the S80 audio outputs from the input mixer
and the noise stops.
There's some kind of circuit going on (ground loop?), because some of the
digital noise is coming from the computer. When I perform actions on the PC,
such as moving a scroll bar, I hear associated noise. Noise is also coming
from the PC monitor. When I turn it off, the noise drops considerably.
This noise does not occur when the S80 power is off, but if the S80 power
cable is plugged in, even when the S80 is turned off at its power switch,
the noise occurs.

There's a midi connections from the PC to the S80, but unplugging this makes
no difference.

Does anyone have any ideas? Could the 1/4inch phone jacks from the S80
outputs be acting as aerials, picking up the RF from the PC? Can I stop them
somehow?

Thanks.