Coils still have mounting points...

And, under lots of torque, you would get pressure on the rear coils to compress them.

As you have opened the diff and found a chipped spider tooth, I would lean towards overall carrier bearing issues. The metal fragments in the oil make for good grinding compound.

Is the play in the carrier, spider gears or pinion?? A lot of play in the carrier indicates the backlash may not be set correct.

I have experienced a cracked bearing race on the pinion that was troublesome to isolate. That provided a clicking sound that varied with speed.