I just finished building my first guitar and everything works fine, except for one thing. When I touch the selected pickup's height screws (and also the pickup rings, as they are metallic) I get a loud hum. I experience no hum when touching the pickups themselves, or any other metal parts of the guitar. The guitar is rear routed, and uses three single coil pickups. The pickups have a metal base plate, which is grounded. The pickup height screws are then attached to the plate, so shouldn't they also be grounded? I can't really seem to figure out what is wrong.

Thanks for any advice
I can think of only 2 things that would cause this.  1 is that the pickups were potted so the screws are touching wax or shellac and not metal and are therefore not actually grounded.  This is highly unlikely but it is possible.  2 would be that you accidentally wired the pickups in backward so when you touch the metal parts around the pickup it goes to hot rather than ground.
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