I've had the same problem with a few guitars, worst was a Japanese Strat. Shielding
doesn't help at all, unless you ground it and stick it to the front of the scratch plate
rather than the back! Best solution we found was to treat it with Rain-X windscreen
treatment(from Halfords etc) It is an anti static coating and more long lasting than most
as it usually has to contend with wiper blades. Doesn't last forever but certainly helps.
Top Tip: RAPPERS. Avoid having to say 'know what I'm sayin' all the time by actually speaking clearly in the first place. (Viz Comic)