Make sure it isn't happening with you TV on only. I find the same thing with my Parasound amp. TV on, hum, TV off, no hum. Some after market PC's such as PS Audio's nicer ones have a removable ground pin. Also, Ernie M (Subaruguru) sells a PC that has a disconnect on the ground. You can then use a good quality PC rather than put a cheater in the mix. I suggest the cheater as a cheap way to check if this is a potential fix however.
Rotel 5 channel amp causes hum through speakers
I have a recently purchased Rotel 200 wpc home theater amp which is plugged into a dedicated circuit through a monster- power line conditioner. There is a low hum through all speakers, which are Thiel 2.2 mains & thiel scs center & rears. The center is mounted right above my samsung dlp tv. All plugs are grounded, and have line conditioners. Help?