Thought it was about time I posted what the problem was so here goes!! The noise was due to the fact that the cambelt idler puller was hanging off! The cambelt jumped few teeth and engine was knocking its tits off!! The cambelt had worn half way through also. I was seriously lucky she didn't go bang!

all good now think I might use some loctite next time I do a cambelt!

do you have the correct/modified timing belt kit ? do a search on the subject the 300tdi came out the factory with a fault causing the belt to slip off and rub the cover stripping it to half the size ,just a thought