Strange topic, but bear with me...

My setup:
- Via EPIA MII12000, Hauppauge 350
- Knoppmyth (of course).
- Internal HDD for OS, music
- External 400GB HDD on firewire for video, recorded tv
- S-video output from MII and digital audio via RCA to Okyo Amp.
- 5.1 speakers from the Amp. The sub is active, crossover freq is 90hz.
- LCD TV and Projector via component video from the Amp. yum

The external disk stops when there is no activity for a period.
When something happens, like a program being recorded or played back, the disk winds up (is very quiet so you can't really hear it).

While the disk winds up, you can hear the windup noise through the subwoofer - that is the sub is playing a noise just like a disk winding up. Somehow, a signal is leeching to the sub.

My guess is its one of the following:
- some signal leaked to the power by the disk - I've moved the sub power plug to the other side of the room, but the noise through the sub is unchanged.
- something inductive around the firewire cable - so I moved it as far as possible from all other cables. Noise unaffected
- or a fault in the Amp (no idea how the noise is getting to the amp in the first place). None of the other 5 speakers is making the sound - just the sub. The sub is closest to the PVR/Amp/HDD.

Any ideas on this one would be most appreciated.
Paul