93 Dakota binding/poping when backing up
 

I bought this truck with 120k on it now it has 187k. I do not go off road or otherwise abuse my truck.

I have rebuilt the engine, AC, transmission, transfer case, ball joints, upper control arms(threads came out with ball joints), drag link and all regular maintenance.

Almost everytime I back up there is a binding/poping noise that can be felt inside the cab. It sounds like the rear shoes are grabbing (we all know that sound) but it is not the brakes. I cannot tell if it is in the front or rear. I have looked for this problem for 3 months. I am starting to wonder about the front or rear diff..... If you have had this problem please let me know.

the last thing I replaced was the U-joints but the (ping) when put in drive came back after a week. I will inspect them in the next few days.