Has the lube been changed before ? if the lube as miles on it, it is very normal, if there has been a recent oil change done, it may still be normal, but watch it.
the rearend has never been apart, i changed the gear oil in it a few thousand miles ago and i didnt notice any flakes, but it was perty dirty. im driving it to the beach next week and since i had some gear oil left over i figured id go ahead and change it again.