After checking the obvious things as noted in the above posts (connections, ground loop problems, bad tubes, etc.), try biasing the tubes. This is tricky and should be done by somebody who really knows the BAT VK-60 (it is not completely autobiasing, there are taps underneath the amp that can be adjusted). While you are at it check the wiring to make sure everything is where it should be. I had one that went to many different homes and one of the wires had become semi-undone; it was amazing that it still worked.
Also, you should really get a true balanced preamp, not one that just has balanced connectors like Rotel and maybe Adcom. This is an excellent amp and deserves much better than the Adcom.
