'Tappity' sound could,just possibly,be the bloody tappets! Going quiet as oil circulates...removing and cleaning the oil spray bar will help to make sure that they get oil as soon as possible.Some say that the holes that the oil spray's from beniefit from slight enlargement.
Best practice suggests that the tappets should be set a touch wide,to aid a decent idle.
Another possible is that you are hearing the fuel injectors clicking away,'they all do that,sir!'

Youth is wasted on the young.