FidgetStone pretty much answered your question since his 2005 doesn't hum. The newer Tributes may be a good indication of whether the G&L's still hum, so whoever has a later Trib is more qualified to let you know whether it's shielded or not. If my older L2K does hum, then it's something I haven't really noticed. There was some copper paint on the bottom of the cavity, but not a full shielding.
Anyway, shielding ain't that hard to do. If you're going to spend 1200 on a bass then spending a few dollars on shielding tape ain't gonna hurt.
