I don't think the fx send level will have any effect that give this background noise. More likely a cable or a flatcable that is lying to close to the circuit board or to close to the tube sockets.
2B- I have one thing that is loose, one of the power tube leads is broken off and I can't get it out. Maybe that is the culprit. Everything else, in my estimation, is secure.
2B- I have one thing that is loose, one of the power tube leads is broken off and I can't get it out. Maybe that is the culprit. Everything else, in my estimation, is secure.