I didn't notice a noise coming from the engine during my test drive nor during the first 2000 miles or so. But after about 2000 miles a new sound has developed or maybe that's just when I stopped playing to radio so lound and began enjoying the sound of my car. Aside from the usual engine and exhaust rumble, you can hear a pumping or flickering noise (if this makes sense) coming from the engine. It speeds up as you accelerate and is less prominent when the engine is idling. My brother says that this is just the sound of the valvetrain, as his friend's M3 makes the same noise and it's normal to performance German cars according to him.

Does anyone know what I'm talking about here?

 

No one???? Someone, go drive around, listen to your engine, and please report back. Help!

 

I can faintly hear the valvetrain in my 500. It's a very light, almost pinging sound. Very normal. There's no way to tell if what I hear is anywhere near as loud as what you hear. If what you are hearing is loud enough to cause you concern, it can't hurt to ask the dealer. If I had to bet, I would say your noise is normal.