As I'm slowly getting acquainted with this amp, I'm coming across new issues which need to be addressed. This 1987x has a master volume installed pre-PI, right after the effects loop between W3 and W4. The pot is installed where the indicator light used to be. It's got twisted leads to the pot (not shielded unfortunately) and the pot terminals are rotated 90 degrees away from the standby switch. I'm getting a lot of buzzing when turning up the master volume. Even with the input volumes at 0, the buzzing is there throughout the entire sweep of the master. The presence pot is very scratchy as well. Here is a video; I pulled V3 and it was whisper quiet. When I individually pulled V2 and V1 with V3 in, the noise was still there. That leads me to believe it's in the preamp section. I don't think this sounds like 60hz hum which would be a grounding or shielding issue right? From examples I'm finding on the internet, it sounds like the filter caps need to be replaced. They don't show signs of degradation, but what else could it be?