Hi, I have a MK6 and it does crunch at times. My sisters Focus 03 plate mk1 i think also does this but alot more often. I read that it only happens when the car is moving. So i tried braking completly untill the car was stationary and then putting it into reverse and it doesn't crunch. But i sometimes cant put the car into reverse gear unless i let the clutch go and press it again.