One other easy D-I-Y thing to try Craig... verify the body of the switch is making contact with the shielding paint inside the cavity. Loosen the mounting nut (1/4"?) and turn the switch just a degree or two in either direction, then re-tighten. I had a very similar issue on my Q-switch one time... turned out to be the shielding, or rather lack of it. And if that ain't it, I'm sure the good folks at Alembic HQ can fix you up.
Good luck, that's a sweet-looking bass.

*ps, if you need some shielding paint, I can send you a little quantity via Fed-Ex. (can't send by USPS) It's not quite as good as the silver stuff they have out there, but has worked fine for me.