ITs probably the tappets m8.

Peice of piss to adjust with a feeler guage and a spanner.

Just take off the ICV and then the rocker cover, put car in 4th and push it back/forward untill the tappets are in the correct place to adjust.
Consult haynes manual.

Make sure theres plenty of oil in the engine as well, because mine gets louder when the oil gets lower. although that wont be a problem so much when i get my zetec in there