A coupe can be made quite civilized
Check for anything loose and make sure anything that could buzz is tied down.
Make sure there are no parts making contact, for example the exhaust is catching on something under certain engine loads.
Fit Carpet.
I have added some DODO matt foam sound barrier to mine with a MLV layer on the front bulkhead and front foot wells, made it so its removable too
My rear bulkhead engine side is an aluminium lined acoustic foam, altho this needs refreshing as its getting a bit old now.
I feel I have a good compromise between weight and sound deadening at the moment.
I do have some stick on sound deadening which is more for panel vibration, it depends what sort of noise you are trying to eliminate to what you need to use.
try deadening.co.uk they have some deals on some of their stuff. Be warned it can add up in cost quite quickly.
Neil