A Class, A160 rattles @ 500kms new

My A 160 Avantgarde w/c I imported from Stuttgart to the Philippines started to have rattles on the underside at 500 km mileage since new. MBenz dealer in this country has no idea...any help??? It seems the plastic cover on the car's underside is the culprit.
Whats the best thing to do? where do i start...im sure its somewhere underneath.

The "A" class hasn't made it to the U.S.A. yet but if you can hear rattles then you can find rattles!! Start where you think you have heard the noise. Look around for items that could cause any rattle, like the underpan.
When do you hear the noise?? Over bumps or from the exhaust when the car is running?

The rattle can be heard when i pass roads with worn out concrete where the surface is not as smooth as it should be. However, on very rough roads, no rattles can be heard. It seems the car only rattles when the road is a "little rough" - some sort of a vibration. If its the underpan, what should i do with it? insert foam in between?