Hey guy's. Recently picked up a 1975 Fender twin reverb. Guitar signal sounds great through it but it has a strong hum. Mostly at zero or max volume. Has a sweet spot at 3.5 where it sounds amazing. I've re capped all the electrolytics and coupling caps. Touched up solders and swapped tubes like mad. I have VI pulled as I never use the 1st channel. Loud hum at zero volume. Any ideas? All plate and bypass resistors replaced as well.