How many miles on it? You could have a bad u-joint if your lucky or the rear end could be the problem, carrier bearings. The only other thing I can think of in the rear that could be vibrating would the the driveline under spring wrap. If you have a cracked leaf or worn suspension, that could be the problem as the diff is moving in a wider arc under heavier load which pulls it out of alignment with the opposite end and then vibrates.Hey I have a 2000 7.3 and when I accelerate hard from a stop there is a vibration coming from the rear. Almost feels like it would be the tires but I replaced them and still does it, any suggestions as to what it could be?