Try it on a diff power outlet and see. Or, a better idea, get a UPS and see if that corrects the issue.
It's quite possible, AC power out of your wall is never stable, it's constantly fluxing, to small degrees that normal surge protectors don't protect you from. It's expected and won't kill your electronics, but it is hard on them. Getting a UPS, the AC power gets converted to DC, which is nice, stable and flat, and then sends it to whatever is plugged into it.