I have a late year model 91 D250, 2WD, 1 owner since new and this truck has a under dash rattle that I can not isolate. I have taken the glove box out and can find nothing that appears to be loose. It is really bad in the cold winter weather. Warm weather, not noticeable. Is it just the flexing of that large one piece plastic dash assembly? It sounds like something is rattling against the dash, but I can't find anything under there to rattle.