Frankly, there's not much at all wrong about the behaviour. The only possible concern might be the drop at idle, but that could be purely a function of the oil itself. What brand and grade of oil did your mechanic use?
Can you hear the tapping while driving, or only when you are "under the bonnet"? It's possibly a dirty lifter - try some Nulon "Lifter Clen" (I think that's its name). Otherwise its probably piston slap, which is a sign of engine wear.