tapping noise

I have a 1988 mk I golf cabriolet and recently it has started to make a loud tapping noise when the engine starts.  On accleration the noise quickens like that of the tappets.  The oil level is fine and the rest of the car shows no other symptoms i.e. lack of accleration.  My first thoughts was the problem was associated with the tappets but before i start looking into that if anyone has any other ideas can you let me know?  Thanks