I could not tell you exactly what happened but I was getting off the highway and went about 5 miles down a residential road, when my truck just starting making a horrible noise. The only way I can describe it, is that it sounds like something fell off the bottom of my car and was being dragged along the road. I checked under my car and nothing at all dropped, the car has a weird light smell coming from it. The sound gets worse if I don't hit the pedal, or if I brake. If I step on it, then it levels out until it hit 40mph then it begins to make that noise again. I don't know if it is something has silly as needing tranny fluid, but I don't know if it could be something major too.