Interior noise

The first mini van I have owned is this 2005 Grand Caravan Stow and Go. I interior is much noiser than I had expected. Anybody installed sound dampening material behind the interior panals or tired anything else to make the interior quieter? I run it with the third row seat stowed. Will there be less noise with the seats up? I also have extra carpeting in the back which may help. Or is this just a characteristic of mini vans? Thanks

Its the cheap plastic they use for the interior.
Sound deadening and a quiet ride must not be in the GC engineering book.