Changed to diff fluid 3 races ago. Just noticed a grinding noise from the rear diff during hard breaking only. Rolls great forward and back. sounds fine when under power in forward. Sounds like ring and pinion skipping but dont know why it would start doing it now? The truck is a little over 2 months old and has been raced only about 10 times, no bashing. took the rear apart but didnt see anything falling apart, loose or metal shavings anywhere. Ideas?