I found the rattles in the back right to be the latch for the rear seat. Find something to rap around the metal latch on the floor so it does not make direct contact with the metal latch on the bottom of the seat.

To fix the plastic sound near the right / rear quater panel, check the seat belt buckle and make sure it is not hitting the plastic interior trim. My buckle on that side for some reason is turned around so it is easier then the other side to touch the plastic trim.

Good luck