OK, obviously you're getting electrical interferences, your HT system seems to be in line with other applaiances in the house. Funny, usually a power bar surge suppressor should help suppress electrical interferences.
I beleive your next step should be to get a dedicated AC line from the circuit breaker box to your HT system, unless your handy, you might want to call an electrician and have that done. I can't think of anything else that would help your situation.