Sound deadening!
Might do a few pics sometime but here is a good tip that has quietened my car no end.
Under rear seat.
Lift up the seat squabs (what you sit on) You will see bare metal, well sorry painted metal.
I had some left over Dynamat so placed this on the metal to cover as much as I could.
(Needs a bit more to fully cover)
I also had some sound deadening mat from old cars but I guess you could pick some up from a scrappy.
Put that on first then laid all the cables for amp/sub/cd on top and another layer of thinner mat on top to cove whole area.
This has made a great difference to the noise inside the car!