Update: I was able to "fix" the piece of whatever in my fork by squirting some cyanoacrylate (crazy glue) into one of the vent holes, then I shook the CA and the loose thing down to the bottom of the fork blade and laid it down with the holes facing up. No more rattle! Of course, I dripped some CA on the floor, and walked in it with bare feet; I hate the stuff actually, because every time I open it, I end up with fingers stuck together, drip it on my clothing, etc. But it can't be beat for a job like this.