Civic dash rattle + mystery bolt

A couple months ago, a bolt suddenly appeared on the passenger side carpet of my 97 Civic HB, under the dash. Now I have developed a
noticeable rattle somewhere around the glove box when I go over a big bump. Even when I empty the junk out of it! :-)
The bolt is black, hex headed, about an inch long, and has a lock washer and a flat washer on it. Before I try and squeeze myself under the dash to take a look, has anyone else had this happen? Any hints on where to check first? Thanks.
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