i had this too. mainly when i am on an incline ro turning from a dead stop. took it to the dealer while still under warranty, and they changed the clutch packs in the rear and i think maybe even the ring and pinion. that was back in early 07 and it started doing it again about a month ago. this is in a 2004 f-150 4x4 extended cab.

 

I get this when slowing down to stop or take a corner. Sometimes when I accelerate it happens again. Almost like something is movng forward or seating itself and then returning to original position. Have checked everything that could rolling around loose inside and out but it is still there somewhere!

 

SD Man -

Do you know what they found was wrong with the leaf springs? I can see my dealer's reaction when I go and tell them that it may be in the leaf springs!!!! I would like to have some facts, or what was wrong with yours so I can see if it might apply to mine.

 

My 05' does the same thing. When turning, get a popping which sounds like in rear. I can rock my truck hard side to side at the bed and it pops. It sounds like leaf springs or maybe shocks. The rear axle doesn't act or drive funny to make me think the clutch packs are bad. My truck is paid for so the S.O.B will have to **** me off worse than this to take it in.