This humming sound has been going on for a while now, and its starting to irritate me. It only starts up when I drive for an hour or so, if I drive short distances, I hear nothing. I dont feel performance loss or anything funny. When the humming starts up it becomes more high pitched when I accelerate, and I can hear when idling. It sounds like its coming from the rear of the Jeep but I haven't been able to figure out where its coming from, I dont want to spend 200 bux on a new fuel pump if i dont need it. I never have trouble starting the car.