You're right.  However, no...  in this case, the circuit is kosher and everything is shared on it.  Even with just the Lunchbox and nothing else, it does this hum.  There's nothing that would cause field interference, either.  My other Ibanez 540RHH and Washburn N4 don't have this problem.  For the life of me, I can't see what the factory did differently than me.  I can't see the big difference.  Clearly, I'm missing something, though.

I think there's something I'm doing wrong in the guitar.  I just can't figure out what.