I installed an amp and replaced all 6 speakers recently, the result was great sound quality with plenty of rattles, especially from the rear. Seeing as I'll be installing a sub soon, I decided to do a bit of soundproofing on the cheap. Rather then waste money on Dynamat or Brown Bread, I went down the local hardware store and picked up a 10M roll of Flashband for 13 quid. Its bitumen based and is adhesive on one side. I covered the whole of the underside of the boot lid (nice 'clunk' when closed), the firewall between the rear seats and the boot, the underside of the rear speaker shelf and the underside of the rear plastic speaker cover (where grills are).
All my speaker vibration has completely disappeared from the rear, and surprisingly, all the rattleing and banging that the FTOs rear end is prone to is also gone. Its comparible to the change in feel when swapping out an old set of droplinks.
I have a good bit of Flashband left over so I'll be doing the front doors this evening to remove some minor vibration at the front end, hopefully the same result can be achieved.
Its the best 13 quid I ever spent and its a worthwhile exercise if only to help dull down the FTOs noisey ar$e
Ciaran