It appears that an iso transformer may be the answer to this problem. From what I've read, the iso transformer will take care of external AC noise, voltage fluctuations, and DC finding its way into the house. I'm first going to call the power company and see if they can do anything. Does anyone know if there is a maximum allowable voltage swing that the power company must maintain within established limits for residential applications? If the problem is DC finding its way in, can I hold the power company responsible for rectifying the problem on the assummption that its a safety hazard? I'm guessing this is a somewhat unique problem given that it occurs intermittently.
Thanks for all the helpful responses.