I recently bought a used MIM J-Bass, and it hummed unless I was touching the control plate, knobs or bridge. I'm going to replace the pickups and pots (two stacked pots, and a series/parallel switch), and I've been advised to add some shielding while I'm at it. From what I've read on other posts, I know I should shield the control cavity and the back of the pickguard. What about the pickup cavities? Is there anything else I should be looking at (or be cautious of) while I'm replacing that stuff?