I've noticed that if I open the window fully in my 04 Vibe, and lean my arm on the top of the door while driving (where the bottom of the window is), I hear a sort of slight plasticky "crack" sound, as if the plastic around the door/window trim is moving slightly or loose, and is moving a bit when I lean the weight of my arm on it. I can't see anything happening though--nothing deformed or visibly bending when I put my arm on the open window.
I don't get any sound whatsoever if I do the exact same thing with my right arm on the other side--that side feels more "solid". Are there any parts in that driver's side area that might come loose, and if so, is there some kind of simple way to get at it and look?