soft mounting the hard drives works very well. The easiest way is to suspend them on some kind of elastics stretched between the sides of the case. I did my soft suspension differently because I wanted soemthing more secure. I mounted my 3 hard drives of gel blocks. There is a pic of my custom made HDD rack below. There are other things you should do to quiten the PC. The most important is to change the stock cooler on the graphics card to something like Arctic Silencer or Zalman HS. You already have a new CPU cooler and quiet fans. Get some soft mounts for the fans. PSUs can oftem make a lot of noise, you can consider changing it to a quiter one like Seasonic or Antec NeoHE.