The graphics card will by far the be loudest, followed by the cpu fan if its stock, then the case fans and then the psu fan i expect.
Check this by stopping various fans to determine which are the loudest.
You will need a new graphics card cooler and a fan controller to start with.
Installing a new graphics card cooler voids your warranty unless you can keep the stock cooler and fit it in such a way that you can't tell it was ever removed.
Theres an increasing number of aftermarket graphics coolers now, i used to recommend the ac silencers but now that the voltage regulators and various other components on these cards get so hot they need airflow, so one of the zalman coolers is probably best. You could also look at the arctic cooling accereo x2, but imo the design is stupid as the fins point towards the mainboard.
If you don't want to void your warranty and can't fit the stock cooler back on in the event of something failing, you're pretty much stuck courtesy of the atx specification which predates heatsinks in computers let along heatsinks on graphics cards.
Either buy a new card (and you'll have a hell of a time finding one thats quiet), or buy some earplugs.
