AD30HTC Channel 1 preamp noise

[mrw_77]

Hi everybody! This is my second post.

Regarding my AD30HTC:
When I first got the amp, I noticed how quiet (nearly silent) both channels were, (as far as hum and hiss are concerned) even with all the controls cranked. Channel Two is still extremely quiet in that respect. Channel One however has quite a bit of hiss, hum and popping throughout the range of the controls (with the noise increasing as the controls are turned up). The amp has a new full set of JJs in it. I tried the old Sovtek preamp tubes in Ch.1, but that didn't have any effect on the noise. I took the chassis out of the head cabinet to poke around. The gain pot crackles when I adjust it, and the hum gets much louder when I put my fingertip on C1 (brown silver mica capacitor) where the Ch.1 gain pot is soldered to the control panel circuit board, or on C3 (gray plastic box-shaped cap) on the main board (where the leads from the Ch.1 gain pot go to the input of V1).

Does anybody have any idea what might be causing the problem and what to do about it?

Thanks & Happy New Year!