I got an 03 coupe.

And my passenger door rattle like metal hitting each other or like keys hitting each other sound (no its not my keys ).

I did a search on the forum, no similar issue found

I can reproduce the noise just by hitting the inside of the door.

Any ideas how to fix it ?

 

Take the panel off and look inside.

 

It's easy to take it off?

 

You need to be careful with it, but it's not impossible. It could be something entirely easy to fix yourself, but you won't know until you look inside.