Have you had the bonnet up and reved it to see if you can trace the noise you any rough location in the engine bay??
Noisy timing chain? Could be the tesioner playing up. Noisey injectors, they all are tho.! Is the noise comming from the head, bottom end, turbo??
It may not be anything to worry about as they are noisey lumps anyway but def worth some investigation. :?
J.