You don't by any chance have you audio system touching your video system, do you? Even if your tv is plugged into the same circuit as you audio, you can pick up a ground loop hum. I had a similar problem and it drove me nuts, I tried running dedicated lines, all sorts of power filters, but it wasn't until I put a MIT Iso-LinQ on my incoming cable line that the problem disappeared.
You could also lift the ground on one piece of equipment at a time until you find the offending component.
Good luck,
John
You could also lift the ground on one piece of equipment at a time until you find the offending component.
Good luck,
John