WTF is this crap in my diff???

I've seen shavings like that left in axle tubes from the manufacturing process before; they were in a Dana 70 on a Dodge 350 4x4.
That's a discouraging hint at quality control.
I'd presume those are leftover from part of the machining process...but, I'd sure probe deeper.

In the case of that Dodge, I pulled the diff cover and drain plug/magnet and axles, and, finding no ground powered metal, sprayed everything out with brake clean, re-assembled and carried on.

 

In any case all it would take is a couple quarts of rear diff fluid and a few hours to remove the third and axles just to look.