Ford Mustang rear car noise

Have you checked the fluid level. Again? Imma Jeep CJ kinda feller. With Jeeps (Trac-loc) Positive traction system, a special additive MUST BE added to the Gear Oil (for the clutches within) Some Gear Oil have it built in, but read the label to be sure (Penzoil used to have a line with it in there already), Is that the case with yours? I do not know who built your rear, but so many times I have seen they do not SHIM the pinion (bearings) as to mate with the Ring in its Quietest Mesh. On Jeeps there are (+) and (-) and.000 (thousandths) stamped on the sets. Briefly and throwing wild #s, if you replaced a +.004 with a +.004 set, no adjustments with shims are necessary (re-use what you had). If you had a +.004 and replace the set with a -.002. Shimming would be necessary to get the pinion to line up in it's "Most Efficiently Quiet Position". I have been told they run the sets at the factory on a machine to determine the best position of the pinion in the the rings gears, then stamp them. Seen too many just slap stuff in, no checking the SHIM charts to do it properly and even using an impact wrench to torque stuff, to "Whatever Feels Good" not to specs. I feel the Auto Engineers had reasons to require these standards over Goober Pyle of Mayberry, who says "It'll Work Okay". Another thing with the Jeep Trac-Loc is, they say if it is making popping sounds during turns--The clutches are not lubricated well. They suggest in an abandoned parking lot, NOT HAULING BUTT! (Cops and such) Do real tight figure 8's over and over, this will make the diff go thru full cycle and lube the clutches. It did work for me and CJ # 4 for me.---Whachu Think?--The Medic