Fender Jaguar making lots of hum and crackling when I play - help!?

I recently put copper shielding on the back of my scratch plate and reattached the grounding wire to the bottom of the trem plate, as per the wiring instructions, but there is still a minging hum and a crackling / buzzing noise when I play, which goes away when the resonance dies. It's not buzzing from an improperly set up bridge, I spent an age sorting that out and it's fitted with the buzz stop, so it should sound great, but something isn't right somewhere. I've tried it in a couple of different amps (ENGL screamer 50 and some nasty Crate thing) and removing it from the pedal chain, new leads etc - so it must be the guitar. I don't want to take it to an expensive professional if it's something I can fix myself - any suggestions as to what it might be anyone?? Its a CIJ 1993 Jaguar with Seymour Duncan Quarter Pounders and a Mustang bridge.
 
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