What is happening is that the little motor in the furnace and the bathroom fan are emitting little radio signals when they turn by having little contacts on the shaft that bounce about, those little sparks are radio frequency creators that the TV picks up, remember the old engines with points and some stations all you picked up in the cars radio was the noise, rev the engine and the noise changed to a faster higher frequency? Same thing here.
Go to an electronics store and ask for a radio frequency suppressor, the ferrite units work, some times you need a capacitor, that is harder to install.
navegator