Well for sometime my truck was making a shutter, at first eveyone on her told me iut was my drive shaft. I checked my rear end fluid it was a little low, add some and also but that firiction mod. in there that it calls for. That helped a little but it was still making that noise when u got of the gas and u could feel it in the floor. well I just bought new tires 275/70 17's goodyear AT/s nice tire works great. well iI put them on yesterday and drove it around and guess what no more noise. The tires that came from the factory were out of balance. That what I'm thinking becouse I drove the truck about 100miles yesterday and no more noise.

 

I'll bet it was the friction modifier that fixed your prob. If you have a Ford LS and don't use it your dif will chatter when you go around a corner. Takes a while for it to work into the space between the cluch plates and do its job.

Been there, done that.