WHEN exactly was the last time that either of your differentials was worked on, particularly the one that had a ring and pinion replaced?

Have you driven it much in 4WD since that date?

WHEN did it start to do the popping?

1977 CJ-7, fiberglass body, AMC 360 w/ headers, DUI ignition, Edelbrock intake and Holley 4150 carb, TF999, Dana 300, 4.56 gears lockers, York air comp, 4" susp lift, 2" body lift, BFG 35" M-T tires, Megashifter, AGR pump & box, REP8000 winch.