There is nothing wrong with your carseat, the noise comes from residual products from the manufacture of the carseat. As you can see from a closer look around the car seat, the majority of the parts are joined with pop rivets and not screws. This is because, from a construction and strength point of view, poprivets are a more advantageous joining method. When popriveting, the parts of the poprivet that are not needed drops and sometimes these pieces unfortunately falls into the car seat, this does not affect safety.