I've had a PSW404 for about 5 months (to go with the SurroundBar) and just recently moved into a house where the room that contains the sub is much more quiet (as long as the kids are asleep). Now I notice an audible and annoying hum from as close as 10 feet away while nothing is plugged in except the power cord for the sub. I've tried other outlets and the thing still hums away. The sub otherwise works when a souce is applied. Incidentally, my big SVS in my home theater hums a small amount too but you've got to put your ear literally on the sub to hear it. Any thoughts? Thanks a bunch!