If you look inside of the front door posts of most new cars you will see styrafoam is used for insulation. It is the best and cheepest way to cut down noise. You can shape it any way you want to by using an electric knife. then fitting it into the space. It can be purchased in blocks or flat sheets in any thickness. I did this in my back wall behind the seats at 1/2 inch thickness, tappering of to nothing at the top where the storage compartment started. If you feel that you want to go upscale you can always buy the black foam insulation that are used on piping inside of houses. It costs more and is heavier but will do a little better job. It comes in flat sheets as well but is a lot harded to cut to fit. Barry 6012