Every once in a while i get a wierd noise that i think its coming from the drive shaft but not sure. It only does it when i'm cruising down the road and the truck speed i guess you can say matches the enginge speed( truck is pretty much coasting on its own and there is no accelerating or decelerating force on the driveshaft from the engine). The noise is very faint and almost sounds like tires on a concrete roadway or bridge. If i accelerate slightly or heavily or get off the gas it goes away. Truck feels fine and drives normal so i'm guessing its not a problem but is it a warning of something wearing or is it something that just occurs.