#1
Recently my guitar developed a strange hum, sounding like when you touch an input cable that isn't plugged into a guitar. This sound persists across a variety of amps and cables. The sound stops when I touch the strings or metal on the guitar. I thought this would be a grounding problem, but I took it to my local guitar guy and he says that after testing it, taking it apart, and checking the wires against schematics - everything appears fine with the grounding on the guitar.

It's single coil, but I know the noise that comes with that and this isn't one of them.

Another mystery. The hum becomes noticably louder when I turn DOWN the volume knob until it gets to about 2 when the guitar becomes inaudible anyways. It also does this when I turn off all of the pickups (its a Jaguar.) Any thoughts? Might I need a new pot?

If it helps at all my volume knob has always seemed odd to me, sound basically disappears when I get around 6, it isn't a gradual decrease in volume, turning it down at all lessens the sound very noticably. Thanks for any input.
My attempt at gear-
Fender Jaguar (limited edition Cream with gold hardware.)
Goya Rangemaster (1967 Italian Archtop)
Martin SWDGT Acoustic.
Vox AD50VT.
Ibanez Tubescreamer, Wasabi Delay, MXR BLUE BOX.
#3
Actually its a guy who used to build guitars and has helped me out before on a problem, I haven't taken it to the local shop yet because I trust my guy more. I plan on taking it there soon though just in case they have better luck. No I didn't specifically tell him to check out the pot, more grounding, but he says its shielded very well. He checked over all the wiring though and said he didn't see any issues, but possibly its burnt out so to say? Not like physically broken? Does that happen? That would explain why he wouldn't have pointed it out as a problem.
My attempt at gear-
Fender Jaguar (limited edition Cream with gold hardware.)
Goya Rangemaster (1967 Italian Archtop)
Martin SWDGT Acoustic.
Vox AD50VT.
Ibanez Tubescreamer, Wasabi Delay, MXR BLUE BOX.
#4
well. that is a lot of stuff. i'm sure your guitar guy is good.

hhmm...

did he check the Input Jack on guitar. Inside?

are you sure all of your solder joints inside guitar are good?

you are shielded like you said, are you grounded well too?

which Amp? The Vox? That has how many tubes again? Do they look good?

Is any of this plugged into a Power Outlet that has lots of other stuff?

Turning guitar down and sound going up is def wrong.

Edit: Sorry if I missed something...it is late here.
#5
If you turn down the sound and the buzzing goes up, that is bad. The volume knob is supposed to go from the hot signal (your guitar noises) to the ground (the silence) with the turn of a knob. If the silence isn't actually silence but a buzz, it has to be the ground. Either that or a faulty pot. Because if the knob is set to the ground and a good ground would be pure silence, you should be hearing pure silence.