I've finished the overhaul/total restoration of my 1959 Superlead from 1973. It's survived the "deck everything!" test. Full blast, everything on 10, utter insanity. Works fine...except I have found that it's got some bacon frying noise. Turns out that it appears to not be a tube. As long as I have ANY 12AX7 tube in the phase inverter socket, it's got this noise. Changing to a different tube doesn't change it. That's with NO tube in either V1 or V2, either. So it's not from any tube, or so it would seem. What are the most likely causes of the noise in this case? I'm thinking it's one of the three .022 coupling caps. But not one in the tone stack since adjusting the tone controls has no effect on the noise. I think that the one between the treble pot and V3A grid is most likely to be at issue. Do you agree? Or is it more likely that one of the plate couplers, being at a higher operating voltage, is more likely to be the culprit?