No, there is likely no reason for concern at all because a little valve lifter noise in this particular engine is normal until full oil flow is being received by the valve train. When you start the engine on a cold morning the oil is cold and is more resistant to flowing (more viscous). Also, most of the thin layer of oil that had coated the engine parts during your previous drive gradually made its way back to the oil pan. As the lifters become lubricated and the oil warms a bit, the noise predictably goes away completely. After subsequent starts during the day there is no sound because 1) the oil is still fairly warm and flows more freely, and 2) sufficient oil is still coating the parts so as to eliminate noise. I don't live in a particularly cold location, but I hear the same noise for a very brief time (a second or two) on even the warmest days in summer. But in my case it is because the car has set for several days without being started.

Use your instrumentation to check the remaining life of your oil. You can also use the dipstick to manually inspect the oil appearance and level. I would not recommend changing the oil (8 qts synthetic is quite expensive) unless you suspect it hasn't been done in at least a year or your oil monitor is showing "-XXX days. Find out from the previous owner/seller if it is know when the last oil change was done and what type of oil was used (0W-40 typically). Per Mercedes Benz, there is no need to use any additives in your engine.