I just went through this same problem. Most Humm will enter through your powered sub. Unplug the Coax cable going to the sub. If the humm goes away you have a ground loop problem and you will need a Groung loop Isolator.

M80 V2,QS4 VP100, Panasonic 37" plasma HDTV EP175 Denon 975, XBOX 360 Viper speaker cables