getting noise from my audio monitors (Mackie HR824's that usually sound really nice). high pitch crinkle & whine. When I click & hold mouse the sound changes slightly then goes back to regular whine cycle when I let go. Different windows make slightly different noises. I've tried to seperate cables as much as possible. can USB cause this unwanted noise? What about too long of a fire wire cable. I would appreciate any suggestions to remedy this. Thanks.