This problem has been driving me crazy. I made a rack for my 990, monoblock amps, and my HTPCs. Got it all set up and seemed okay for about two weeks and now all of a sudden I can hear my processing and HDDs operating through my speakers. I'm not exactly for sure it wasn't doing it before, but I can certainly hear it now. I've heard of other people having the same problem and fixed it by upgrading their computer hardware drivers, specifically the mobo. Didn't work for me. I also placed my sound card as far away as possible from my graphics card. Didn't work. I also tried an optical cable from my sound card to the 990. Didn't work. I then figured my 990 was picking up RFI from my computer through the air and then sending it to my amps, but with the 990 turned off I can still hear it. It doesn't stop until I turn off all my amps. I was wondering if anyone else has had this problem and what their solution was. I'm going to try two things:

1. Place ferrite cores on all of my power cords and speaker cables.

2. Ground together the 990, amps, and HTPCs.

Any suggestions?

The problems just keep stacking up. I attached my HTPCs to a back up power supply and it greatly reduced the computer noises, but now I'm getting a low hum out of my subs. Apparently I now have a ground loop issue. Back to the drawing board.

Have you tried shielding your HTPC's? While not even close to the same problem, my wife had a problem with her aftermarket car stereo picking up engine noise which I believe was rfi. The installer solved the problem by wrapping the unit in an aluminum shielding. It seems you could try something similar with aluminum foil or sheeting and possibly a wire to ground the shielding.

Yeah, I looked into shielding but the products that look half-way descent are kind of expensive. I am getting closer to solving the problem. I got rid of the hum. The computer noise is still there but not nearly as loud as it was before. I'm hoping the ferrite core cord noise suppressors will completely get rid of it.

I wanted to add another question to this topic. I'm ordering about 40 ferrite cores for my power cords and any cable that transmits digital data. Should I also use ferrite cores on analog cables or would that just cause other problems? The reason I ask is that you normally see power cords and digital cables such as HDMI and USB with ferrite cores pre-installed, but you don't typically see analog cords such as component or RCA with ferrite cores and I was wondering if there was a reason for this.