I hope someone can help me. I have a 1997 4 wheel drive Ford Explorer XLT 4.0L 6 cyl. automatic with control track. The problem I'm having is this: When driving and coming to a stop I notice a "thumping" noise coming from the rear of the vehicle. This only happens when the vehicle is "downshifting" into what seems to be 1st gear. Can anyone give me an idea of what it can be and how to fix it? Thanks.