Team, reporting back here. The culprit was the thread on one of the third member towers. The load bearing side that also has the locker. The thread was beginning to collapse, which lead the backlash to increase over time since it’s one of the places where it’s controlled on the ring side. Picture here for reference. The installer said they’ve seen this on a number new of the 8.2” diffs with locker - says it’s the weak point.

Labor was covered under warranty. Parts weren’t - Nitro does not honor its warranty. Nitro basically said they don’t cover the gear noise and blamed it on the driver. The installer said this kind of customer service is very common for Nitro (beware). So I went with Yukon for new gears. The installer also put some tig welds with my consent to make sure that side does not come off the thread.

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