My car (sorry...not a MB) has rather load valve tapping noises before engine warms up, if the car havn't been run for a few days. I have noticed this on a 2001 S320 as well, except it's quiter and lasts 10 - 15 seconds.

I suspect this is due to oil drain back to sump and temporary collapes the hydraulic lifters, thus causing the noise.

Could someone please confirm if this is the case?
What would be best for the car? Leave it to idle till warmed up or drive it slowly so it warms up quicker? If the car is driven normally during this phase would it cause permanant damage to valves and/or lifters?

Thanks very much for your help..