I was able to do the extension cord test. Used a (probably) 14 gauge 25 foot Home Depot type extension cord. Tried it in two separate outlets: one across the living room from the outlets I've mentioned, one down the hall. NO CHANGE!This test is not exactly like Al recommended,
an extension cord that is long enough to allow you to connect the amp to a different outlet on a different AC run.The important part is "different AC run." "One across the living room" is likely the same run as any outlet in the living room. "One down the hall" may also be on the same run as the living room. The only way to know is to turn off the breaker for the living room, and see if the hall outlet still has power.
I don't think there is any doubt that this is either an amp issue or house wiring issue(just living room or maybe whole house).
IMHO, the best plan of action would be to take the amp to the hi-fi shop you mentioned, then if it works OK there, you know it is your house. Then try the amp in another room of your house, preferably as far from the living room as you can and if it works OK, it's the living room, or if it hums, then the whole house.
You could try a different room in your house first, but if it hums, then you must take the amp to the hi-fi shop for testing.
Good Luck
