The best way to make your case more silent is to get rid of what makes the noise! Some people here seem to drool at fans having 3 or more 120mm fans. Insane! That may be great for cooling but often it's overkill.
Also, I'm noticing most modern cases now have many, many vent holes in the darndest places (under, over, front and backs). All of those holes, while greatly helping keep the innards cool, also add to the noise problem.
I don't see things improving. The P4 is gonna be a b!tch to keep cool. It all adds up to more fan noise. Not good!