Corsair has some great Water Coolers, however they are extremely loud! Almost double in noise compared to other Water Coolers that already out there. Comment above was right, a custom loop is the quietest way to go, or to get a silent case; however custom loop can become extremely expensive and risky if you do not know what to do, and a silent case may not be as sleek as you want, or as effective with case fans.
I myself had trouble choosing a water cooler as I have the NZXT H440 which is silent, and requires water cooling. After careful consideration, I myself chose the NZXT X61 Kraken. It's got a greater performance than the Corsair H100i which was my initial investment, and it's half as loud. You may want something smaller than a 240mm or a 280mm radiator, let alone a 320mm radiator. So I would recommend the NZXT X31 or X41 as they will both fit the same sizing. Honestly, if you really want amazing water performance you need custom loop, but I have a feeling it's out of your budget, so if any of those, go for NZXT or Swiftech. That all is in terms of a brand new cooler, if you just want a quick and cheap way, simply change the fans.
Kind Regards,