I think it's your passenger door window assembly...notorious for breaking.
Pull the interior door panel. You may find that part of it has physically separated (or even flat-out broken) off of the glass.
If there's nothing obvious, just keep that door panel off and drive around for awhile, holding on to various parts of that door to try to locate and stop the source of the rattle. It may help to actually have a passenger sitting next to you!
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