Halcro,
Have you actually documented what's going on at the wall socket during those periods where the sound deteriorates? It would first be prudent to do that, so you are not wasting money on a (expensive) power regenerator. Another reason to do that is to determine the magnitude of the AC voltage swings, if indeed that is the cause of your problem. Because different regenerators will have different capacity to maintain constant AC output for a given variation in input AC. Two excellent brands of regenerator: PS Audio and Furman.
It's also possible that someone in your neighborhood who shares your AC or some household appliance is switching in and out, causing disturbance on your AC line, when switched in. In that case, of course, you need some sort of filter or dedicated AC lines, or both, and not necessarily a regenerator.
