Does something have to be soldered to make a connection or can it just be touching? If it has to be soldered I think I have found the universal problem with most jazz basses that hum even if there is reverse wound pickups. When I took apart my jazz bass I noticed that the ground wire that was going to the bridge wasn't soldered to it, it was just sticking out of the hole touching the bridge. I'm soldering the ground wire tonight and re-soldering my pickups to the pots. I'm glad I finally went to the trouble of taking my bass apart instead of just wondering what the problem was.