Just tore down (neck off) and reassembled my backup bass, a stock Ibanez SR-535. Now there's a rattle whenever I play any note on the B string. Doesn't happen on any other string. Damping the string above the nut doesn't help. Damping the string behind the saddle doesn't help. Pressing down on the saddle to immobilize it doesn't help. It almost sounds like it's coming from inside the string, but if it was a broken core I expect it wouldn't stay in tune. There's also no reason to suspect a broken core, it's only been off the bass for a couple of days and there are no kinks in it. The bass never did this before the disassembly and reassembly. Any ideas what might be going on?