Hi Victor,
Welcome here!
regarding the engine light, I would suggest you to check it out by an official dealer nearby, they can tell you more about the codes.
as for the peep sound, This might be the sound of the reverse engaging, but I dont own a is200d so I can't confirm this.
The metallic rattling can be from the entire exhaust, from your exhaust manifold untill the exhaust tips. It can be something as simple as the heat shield under your car, which hits your exhuast now, you can push this shield away from your exhaust pipe by hand ( when your engine is cold and not running)
Therefore I would suggest you to go back and let them check it out as your car is still under warranty.