I've just had a solid, electric 5-string 'mandotenor' made for me (cross between a tenor guitar and a mandolin) which is in the process of being tweaked and finished by its maker.

There's an unusual amount of noise/hum from the pickup - more than in other instruments he's made - and though it sounds as though it's not earthed, the earthing is definitely there in the wiring.

It's odd, because when I touch the string or pickup with my hand as I'm playing, the hum stops. To me, this definitely sounds like a lack of earth. His solution will be to line the backplate (where we can get at the electrics) with silver foil, and use foil-type paint in the cavities - a technique which he's used to reduce hum before. He's an excellent luthier, but also slightly disconcerted by the unusual hum level. It's been tested on different amps and with different leads - all with a similar result.

I'm just curious as to whether there's a wiring solution to this - if my body can earth the instrument, can anything be soldered in to have the same effect? I've come across this in other, much older instruments and I'm sure it must have been tackled by other people. Ideas and suggestions welcomed.