So today when closing my passenger rear door, I was standing in such a way where I could see the space between the bed box and the cab. When I closed the doo, I noticed out of the corner of my eye, a flap move in that space well below the glass. It seemed like it was relieving pressure/air from the cab? Anyone else notice this or know how it works? Maybe this could be the source of the leak I've seen some people post about if it doesn't close/seal properly.