Sam - you sound like a knowledgeable man for zetec-s's
The car was low on oil when i brought it, the dip-stick was dry - i paid very cheap money for the car due to this fact. The engine has been noisy but hasn't got any worse, and it stays silent up to 6,500rpm and the noise is very light and not the usual bottom end knocking noise, it worsens as it warms up. I might stick some thicker oil in it and see if it quietens down?