Hey, I just bought an Ampeg VT-22 and have some issues with the reverb. When I dial it to about 3/4 it builds up feedback within a few seconds. This is without anything plugged in and the volume at 0. If I rock the amp I hear the reverb tank banging loud and the feedback is gone, but it starts building up again. The reverb is also very very quiet when I play through it. I've read about microphonic tubes and the tank being mounted to tight to the case, but I don't have the amp with me right now. What else could I look for? Thanks!