Trying to isolate the shielding issue on this guitar I have discovered that touching the soldering irons stand while it is plugged in and sitting in the holder achieves the same result as touching the shielding in the pot cavity on the guitar-noise disappears. Is this then mains hum or is the earthing on the adapters I am using not doing its job properly?

http://sound.westhost.com/earthing.htm

may offer insights.