So pretty much when I slowly accelerate from a standstill on flat or uphill ground, I get this scratching/creaking noise from the back end. Sounds like nails on a chalkboard/nails on rust. It only happens for a sec at like 1300 rpms in first, and I don't hear it when I have music on or the windows up, plus it only happens if I accelerate quickly. Unfortunately I drive with my windows down a lot and accelerate slowly, so I hear it a lot. Is the truck just being old? Any ideas of what this could be? Truck is a 99 SCab 2wd. Thanks