metal particles in gear oil from final drives in takeuchi tl140

i changed the oil in my final drives on a 06 takeuchi tl140 with 700 hours. this was the second time i changed oil. old oil came out frothy...with air bubbles. and the old oil had lot of metal "glitter" in it. i installed new oil and ran for a bit and drained it out, and replaced with new oil. ran another few hours and replaced oil again. still see "glitter" in the drained oil.
should i be concerned? running 75w-90 oil. would thicker oil provide more protection?