On my two guitars I noticed a strange behaviour, which keeps confusing me:
Guitar A: Two humbuckers, 3-way switch, 1 volume, shielded with copper foil. When plugged into the amp and having the overdrive channel selected, theres an audible hum when the volume pot is open. The sound of the hum changes when I turn the pot down, until it vanishes completely. When I touch any metal parts of the guitar (strings, bridge, output jack,...), the hum gets much quieter. The same thing happens when I touch any metal parts on the amp or pedal board.
Guitar B: Two humbuckers, 3-way switch, 1 volume + 1 tone; same behaviour as guitar A, except that theres no change in the hum at all when I touch metal parts, no matter if it's on the guitar itself or on the amp or pedal board.
On both guitars I checked the grounding with a multimeter and everything seemed ok. Strings/bridge, switches, pots and the shielding of guitar A are all grounded to the sleeve of the guitar cable.
Shouldn't guitar A make less noise because of the shielding?
Why do both guitars behave differently when touching metal parts on them, or even the pedalboard/amp?
Thanks for your help,