Get out your magnifying glass and check for needle strike marks on the darning foot or the sole plate by the feet. The quilt has to be all up on the table to prevent drag. Drag can pull the sandwich enough to pull the needle off center causing it to hit something. You can also pull the needle off center by pulling the sandwich while the needle is still in the sandwich.
If you are not wearing glasses, put some safety glasses on before you get a needle piece in the eye!