This may or may not help, but I'll relay a similar experience. I had a buzz when the tv was on, regardless of where it was plugged in and the grounding status of the tv (it is 12 yrs old and connected through coax cable tv, and located 0.3-4 m from my audio gear). After changing the location of my various audio components to different shelves, it vanished. I never did figure out whether it was the change in distance of one or more components from the tv or simply plugging and unplugging IC's that solved the problem. Possibly, removing the IC's may have abraded and/or "cleaned" them, or the amp or some other component was moved out of a critical EM field. This may be irrelevant to your case, but might be worth a try in case there is an EM field or RF that is the underlying cause.