Bentley wrote:Intermittent valve noises are normal upon starting, sudden acceleration, high temperatures or high engine speed.
Haynes wrote:Note that it is also normal for the tappets to be noisy for a little while after the first start of the day, and when idling after a high-speed run. Fitting new tappets will not necessarily improve things. Experimenting with the make and grade of engine oil may minimise these symptoms.
Fot the record, I'm running a 20w50 mineral oil, which has just been changed after the first ~2500 miles.