Well, this is interesting and somewhat disheartening. Today, I took my amp apart with my friend the tech, and we were unable to isolate the source of the rattle. We removed the amp from the chassis, plugged it in and heard a sound similar to rattling glass when I played. We took out and swapped around tubes and cleaned out the contacts with zero improvement, until he was completely satisfied that it was not the tubes rattling. He used something to apply slight pressure to just about every component on the board to see if he could find the rattle and nothing helped. Then he noticed that the transformer was not sitting flush and theorized that the amp had taken a fall at some point before it got to me, and our current guess is that whatever is rattling might be inside the transformer! Although, we're still not even sure about that. Luckily, it's not really audible at full band volume and I still love the sound otherwise; just kind of a bummer that it seems like it's not going to be fixed without some more in depth surgery.
Rig: Reverend Roundhouse RT.Joyo Ultimate Drive.Digitech Bad Monkey.NYC Big Muff PI.Digitech Hardwire DL8.Blackheart Handsome Devil