I just purchased a G&L MJ-4 bass on Reverb. It looks brand new and the seller said it's only been played for 5 hours or so. I believe him. The bass is pristine and even the case smells new. I was a G&L dealer in upstate New York before I closed my guitar and bass shop to retire. My new bass has a hum that goes away when I touch the bridge or strings. That is a classic grounding problem, but I cannot find any loose soldering and everything seems to check out. I've played the bass through several amps and the hum is still there. Could a bad pre-amp cause a hum. Also, G&L didn't shield the control cavity, apparently thinking the bi-coil humbuckers didn't require any. I called G&L for help and they said I needed to go to an authorized dealer. Any suggestions?