We were in the midst of doing a quickie alternator change the other day, had pulled the new one out of the box, and were getting
ready to swap the fan over, when I heard a rattle from inside the new one. I turned it over a couple of times, and could see though
the holes in the case what looked like a small pebble. It was too big to just fall out, so I pulled the regulator/brush holder and
shook it out through that hole. I didn't feel like pulling the new alt all the way apart to look inside, as it was right at the end
of the day, plus I didn't want to possibly mess up anything that might jeopardize a "warranty return".

The piece is triangular, like a slice of pie. Maybe 3/4" long, 1/2" wide, 1/4" thick. Very hard, possibly ceramic. Almost white, but
with a greyish tinge and flecks of darker mixed in. Top and bottom surfaces are flat, the two long sides are curved slightly
inwards, as if someone had pinched it with their fingers, but very symmetrical. The sides are also sloped a bit, making the top
surface smaller than the bottom. All edges are rounded, and all surfaces are shiny, as if it's been put through one of those old
"rock polisher" things. No markings, logos, holes, indentations, or glue residue. Nothing to suggest whether it belongs in there, or
got dropped in during assembly. Very strange.