I noticed the other day that the plastic cover on the rear bumper of my '04 XLT was lifting at the corners. When I slightly lifted the cover at the corner of the bumper, sand and gravel fell out. In the Northeast they use sand of this type by itelf or in combination with rock salt to make the roads less slippery. This material however is collecting under the plastic cover. If left, it will certainly cause premature rusting.

Has anyone else noticed this? If not, look at both ends of the bumper and see if the corners appear lifted.