I'm among those who notice quite a difference when my heaters/TV/hot water/microwave etc are all not in service. Just wondering whether this would be a reasonably inexpensive way to resolve that issue.
Some power conditioners, PanaMax, among others include an IsoTransformer with the rest of the powerconditioner jazz..... Mine is a 400va unit which everything but power amps/sub amp is plugged into.
Investigate grounding options, while you are at it.