I battled this issue when I first bought the car 5 years ago. They swore to me the noise was normal. It is a Mercedes engine and they are known for being a little noisy. Even my dad's 1976 SL convertible is a little loud.

After all the noise, my car still runs great 5 years later and 55K miles later. It is noisy at startup but after it warms up it gets more quiet.... but still a little noise. This is normal as long as it isn't really loud. I actually like the noise... reminds me it is a German machine.