One of my co-workers is a kick-butt player, but is GAS free and has never done his own setups. He's one of those technically excellent players that doesn't dwell on the hardware. I stopped by his place Saturday to do a basic setup on his only bass, an older Ibanez P-J with active tone. All went well except for a persistent rumble in the electronics I can't find. It has a brand new battery, and we tried several. It doesn't appear to be a grounding issue. It was only affecting the J pickup at first, then I cleaned the pan pot and it started affecting the P pickup instead. I cleaned it a second time, and it was back to the J pickup. I tried checking for loose connections on the board, and the best I could do was induce more rumble when I touched two capacitors (by adding hand capacitance). Any ideas? A new bass isn't in the cards for him right now, and he's trying to start gigging again after a marriage and baby break.