Finally wore the old ones out. Admittedly I don’t ride the mountain board that often but the original ones (on the left) lasted 3 years and still didn’t fail catastrophically as the original steel ones did (wore those down to nubs in 6 months)
So I am declaring Delrin the greatest plastic ever
Definitely uneven wear, tilting, not enough greasing, or wrong aligned sprocket increasing noise, but difficult to say how much. Each of this described issues can have different influence. Worst case is combined all of it. My experience is that sound of my chain drive correct assembled have nice cultivated sound. You should not hear big metallic sound.