Waffling sound inside my Pacifica 2018 Touring L van when you first open any door, especially when its cold and hasn't been started yet ? Van only has 18k miles on it . Sounds like ( picking up a long piece of cardboard & shaking it violently ) . Salesman thinks its the Perimeter Approach System . Dealer hasn't a clue ? Sounds like the floor airbags inflating ( if it really had floor airbags ) ? Another 2018 Red Touring L did the same thing when we went to test drive it ? Any ideas ?