I'm a big fan of dynamat, quality is bar none. Now i know this is not stereo related but this is exactly the same thing(sound deadning). Pretty much put it wherever problem areas seem to be.. or even better(cost dependant) everywhere and anywhere you can (cover ALL holes). It will eliminate pretty much any sounds that could be bothering you. There are also a few spray sound deadning materials that could be helpful. Just make sure the surface is clean and use a heat gun to apply it(makes it pliable and moldable).
If you have any other specific questions just ask.
