This could be caused by the synthetic oil because it flows much better and therefore can flow OUT of the lifters overnight much easier than dyno oil did. Consequently, it takes some time for the lifters to pump back up in the morning. I used to own a 1990 300ce that had the 104 engine. The previous owner always used Amsoil synthetic and I thought the car had disconcertingly loud valvetrain noise at idle. I switched to dyno oil and the valvetrain noise subsided significantly. Thereafter I always used dyno oil just becasue the valvetrain noise with synthetic worried me so much.

Greg