Okay, so I know it has been a looong time, but I finally cracked it open again and while I was fiddling with it, one of the wires broke loose. I decided to snip the other one off, restrip them and resolder them both. The noise is MUCH better, so it looks like it was a dying wire/solder joint. The noise is still present a little bit when the connection is jostled, and I could have probably done away with all of it if I had had a suitable soldering jig to work with. In any case, it's so low that it isn't audible below multiple layers of drums, guitars, horns, etc.
Success!
p.s. sorry to resurrect such an old thread!
