I have a '96 4.6l T-Bird with 120k that has developed a groaning vibration in the drive train at between 30 and 50 mph. I replaced the differential bushing and it made a slight improvement. I am thinking u-joints or tranny outputshaft bushing may be shot. The car is fine at highway speeds and I do not want to begin replacing more parts without cause. I also get a clunk on coast down, downshifts which is coming from the tranny tail / floor area. Anyone had a simular situation and possible fix?