I have the exact same problem on the exact same amp. Anyone know what it is? I read it could be the tubes but the amp performs perfectly tube-wise... no weird noises or lack of power, anything like that, they sound great and are very quiet when not playing. I read that someone had this problem and changing the tubes, even the right ones properly biased had no effect on the issue so I am reluctant to try since it sounds great. I bought it used, and have no idea how old they are so they they might need changing anyways. I just don't want to throw good money after bad as I can still return the amp to the seller (they did not indicate any issues and listed it only as used). Any advice?