I've heard noise due to the drives spinning/seeking (I think seeking more than anything). I doubt it's getting in internally to the empeg's audio circuitry though. I think it's producing some small current fluctuations in the supply lines that are getting into the amps.

It's so quiet I've haven't ever bothered about it, but it definitely was there. This was in my old car and I'm not sure the M3 with factory amp has it. I think I remember the old car having it even before my empeg when I had an embedded PC with a 3.5" drive in the boot many years ago.

The sound is best described as "fluttering" I think.