new. I really think its a ground loop between the pre and the amps. When I used the pre in front of an integrated, I had the same problem. That was mitigated by plugin both into the wall sockets. I cant plug the manleys into the wall sockets since they'll really really hum, and that's w/o the pre. One of the amps went back to the factory and got a clean bill of health and both play beautifully.