Ok, here's the problem. I play a MIM Jazz with Di Marzio jazzpickups in it, not sure what type, but the polepieces are black, with a screwwire-look on the outside and white covers. I play with my thumb resting on the E string, which causes it to touch the "polepieces" in my pickup. Whenever I do that, I get a hum from my pickup, that increases if I turn the volume of my pickup. If I play bridgepup only with my thumb resting on the neckpup I don't have any noise, and vice versa. You get the deal. Someone told me this is normal for all Jazz Basses, but I don't believe that. My guess it's a grounding issue, any ideas and how to fix it?