thump in the rear 50 ford

While driving my Ford on the highway today I suddenly heard a thud thud thud sound in the rear of the car.... She has a 350 Turbo ****** ....8 inch Ford rear end.... Any ideals where to start .....The noise stops when you let off the gas.....I was thinking rear end or drive shaft ...... any other ideals ????thnaks guys

 

Check for this
http://www.youtube.com/watch?v=XOvKmUeLvVY&feature=related



L_N_A

 

Is this thing lowered? my 50 did the same thing. Under load the diff rolls back and the tailshaft hit the floor.

 

Got it fixed ....... turned out to be a very bad leaf spring bolt ......thanks again guys