I have a 2005 explorer that has a rhythmic vibration when decelerating. It almost feels like you are going over a little tiny bump on the road. This happens when I let off the gas from speeds over 45 mph or so. There doesn't seem to be any problem when accelerating or braking (although the braking may be getting a little worse). I've looked elsewhere and can't seem to find anyone else with the same issue. Is this just a wheel balance issue?