It's all good in da hood... just pretend your driving a porsche. I still haven't figured it out myself nor have many MBZ mechanics. I've heard people say its related to the timing gear sprocket, it needs to get oiled before the noise goes away, then another theory where the silencing rubber coating on the sprocket has worn away. also if the oil sprayers to the sprocket gets plugged it will make the noise. Then there is the issue of tolerance in the cylinder bore, I know many late model chevy motors with piston slap issues until fully warmed up, none of which are harmful to the engines life. So I just live with it. it only last a couple seconds and then its gone. But I doubt it's related to the valve train.

Also there is a check valve on the driver's side compartment that make a loud ticking sound, completely normal.