I've got one at the minute which you think is inside the car, yet Blue Tack on the external wing mirror cover between the door and the mirror,cures it!
So get someone else to drive and you trace the rattles, even if you have to do what Andy suggested,bit by bit.
Finally, if the above fails get married and those types of noises disappear and another noise appears, best described as a nagging rather than raterling with the occasional phrase from your left as "Are you listening to me"!
