I would look under the actual box. When I had a rattle in my G's box, it was caused by a flat metal piece located inside and under the glove. (I put my hand in the glove and pushed down on the floor, it had some give). It was a little loose, and every time it flexed or bent, it would make the rattle noise. I added some insulation type between it and anything that was loose and it took care of the rattle.