Recapping:

Two common sources of hum:

1. Cable TV.

Solution: Isolate with a pair of transformers back to back, etc. Routine.

2. Differences in ground potential at different outlets in the home due to being on different panels, breakers, etc.

Preferable solution: Try to tie TV to same outlet that equipment stack.

Secondary solution when preferable not feasible: Use an MIW Power, Leviton, etc device in the wall.

I think this might be what I have gleaned from all the posts. I've done service calls for nearly 30 years and have frequently run into cable TV ground problems, but haven't dealt with enough plasma to have run into and solved those problems yet. Wasn't a problem with projo or direct view, obviously.

Thanks to all who have shared their expertise.

=Tom