I've had a Warfedale Powercube 12A for about 8 or 9 years. Its worked fine until a few months ago I woke up to the sound of a loud buzzing noise comming from the Sub. Its not feedback like you would hear from a bad ground, its sounds different and is much louder. I've been using a Pioneer VSXD-912 Reciever with this sub and have connected it with the Sub out jack on the Reciever. However I dont think that the noise has anything to do with the Reciever as the noise happens regardless of whether or not the Sub is connected to the Reciever. All I have to do is plug the Sub in and turn it on and it immediately makes the noise.