My bet is that the backlash was not set at the same spec as it was before they yanked the open carrier. They should have measured backlash at 3 or 4 locations around the ring gear, averaged it, then reset it with the ring gear bolted up to the LSD. Also will get gear noise where none was before by not thoroughly cleaing the areas where the ring gear seats on the carrier and the back of the ring gear. If any debris is stuck in there, it can slightly warp the ring gear enough to cause gear noise.

Unfortunately, you probably don't have a good measurement of backlash before dissassembly. Can't really used the FSM figure as that's for new gears. I had to yank one of my diffs three times to trial and error the backlash and get rid of gear whine. I thought I was going to save time by having a "gear expert" set it up for me. But I had to completely redo it without the original backlash figure. Finally got it right by setting towards the loose side of the FSM range.