I have this weird kind of humming from one of my basses. It has a P/J pickup config with volume and tone controls for each. The pickups are not top of the line. When the volume controls are off, it hums. When the volume controls are maxed, it hums, but when I touch the strings it stops a little. When the P pickup is off, the J pickup hums only if the volume is at max. When the J pickup is off the P pickup hums less than the J p/u, but at any volume setting. This really sucks. All the ground wires go where they are supposed to. All electronic components are in good condition. I plan on replacing all pickups in a week or 2 with P/J humbuckers. What should I do to get rid of this humming? Should I shield the electronics or what? HELP!