Do you notice a whine from the drivetrain (specifically the
transmission) at low speeds (10-15mph) and again at around 40mph?
Ford is telling me this is normal after the vehicle has broken in.  I
don't hear it on new Aviators.  

There is a Noise thump from rear of 99 explorer sport after fast breaking. 70,000 miles. If you stop slow it does not happen. If you break fast then ounce you stop completely something in the back area gos a load thump. What could it be? Thank You very much for any reply :)