I have attempted to strip it down, this issue has been going on since I built this HTPC which was 5 weeks ago.
Basically I can have every device plugged into my receiver without any hums at all. I can play music from my phone, and dvd player, and through the cable box. All without any hum at all. I have the cable line grounded to the same power strip as the receiver, sub, tv, and all.
Then I take the HTPC and plug it in. As soon as I plug the HDMI cable from the HTPC to the reciever the hum starts. I have tried plugging the HTPC into the same power strip, and a separate power strip.
I know its coming from the HTPC and the only way to connect the HTPC to the receiver is through the HDMI port so I can get video.