nocking from rear td5

hi, i have an 01 td5 auto with 140000 on the clock. noticed today a nocking noise when pulling away from a standstill i think from the rear. seems to be louder the faster you pull away. doesnt seem to do it if you slow down to about 5 mph and then accelerate any ideas. many thanks, alan.

check the rear prop doughnut

hi thanks for that forgot to mention also started at about the same time as the nock when i put it in reverse and when putting it back to drive there is a crunching noise it only makes the crunch when going from reverse to drive no other gear change ie from park to drive. any thanks alan.