Have 2000 SS. Recently whenever I get a hard bump (and that is often, here
in michigan), something inside my passenger door rattles loudly.

It never rattles on nice flat road, it is either a bump or up/down icline.
It rattles very fast - ratt-tat-tat-tat-tat-tat, etc and then stops.

I was thinking door arm or window guide? But the door, lock, window work
fine. And I wouldn't have a clue how to get into the door and what to even
look for.

Any help would be appreciated !

Thanks in advance.