I had the same un-findable rattle in my Spoiler Five, that I too tracked down to the bridge. As I needed to polish it up, I took all the strings off and disassembled it to polish it.
I was amazed at just how many parts and screws there were, but after the Brasso and the BreakFree, I reassembled it and the noise was gone.
Should you decide to do this, a word of advice:
I reassembled mine and replaced it back on the bass, strung it up, and then it dawned on me . . . I'd put it on backwards ! ! So make yourself a diagram as to which way everything is facing (!) and also make a diagram of just where the saddles are along their threaded rods. I just put 'em back on at random, and a diagram to adjust them back to their previous location would have sped up resetting my harmonics afterwards.
J o e y