Just bought a used Classic 30. Sounds good except that there is an audible vibration (not through the speaker) caused by the metal wire type tube retainers that surround each tube. Wondering if anyone has a good way to remedy this vibration. The metal used in the retainers is of the springy type so I don't think bending them is the answer. I wasn't sure if it was safe to wedge something in between the tubes and the retainers, and if so what would work well? I'm new to tube amps and don't want to screw something up with it. Thanks in advance! FM