Is there a chance you could bring the amp to a friend's/ relative's house for testing purposes??

As I have mentioned in other posts, I have had amp hum at certain times of the day...all told, maybe about 1% of my listening or TV viewing (and its at a very predictable time of the day-I sometimes go week's at a time without hum). When I first bought the 7500, I tried everything to track it down..no luck. Who knows, the frequency of it happening since then has greatly diminished. I know another time when the hum reappeared, it turned out to be a faulty old desk lamp that must of been on the same circuit.
As I said in other post, I really believe it originates with the power grid (its a very old neighborhood/no upgrades in line transmission).
I do have DIRECTV; there is a ground wire outside the house, i.e., that I would assume there is a ground rod associated with that wire.

I would really try and move the amp to another location for testing purposes.....