Subaru Forester 2012: Rattle isn't being fixed

First you should get their agreement that there is a rattle and that it needs to be fixed. Then you've got a starting point, from which you should be able to work out a plan of action. You need to impress on the dealer that you are unhappy with the car and with the service you have received, and make sure they understand that you will not go away until you are satisfied.