Thanks! Yes, it is strange. I was kinda bummed when we rearranged everything and found this out. Still haven't tracked down the source, though it is not related to my home's power, at least as far as I can tell. I killed the power at the breaker and was still getting this interference. I live in an attached rowhouse so it might be something coming from a neighbor. Anyway, since it doesn't really happen when I'm playing music it is not a huge deal, as long as I don't have to listen to it when I'm working.