I had a rattle develop in my Z over the winter. Sounded like something heavy rattling around in the glove box, but nothing was in there. I finally noticed when I had the hood raised that the rubber bumber stop on the right side had worn through. I rotated it 1/4 turn so the hood was resting on fresh rubber, greased it up, and no more rattle. I learned this trick from an old Olds 442 I used to own that had the exact same rattle. Hope this helps.
