My new Fender Jazz has a funky problem. I get tons of hum & buzz when both pickups are up full. Isn't this the opposite of how it should work? It seems to be mostly the neck pickup. When I solo the bridge pickup, I get very little hum. But I get lots of hum when I solo the neck. Anybody seen this?
Take it to a repair tech it sounds like you have a loose wire in there somewhere. It is probably a simple fix.
How comfortable are you with a decent soldering iron? You may have a broken wire, a broken solder, or just a solder that's gone crap. I'd say to pull off the control plate and retouch the solders and see if that does it.