The H100i produced modern vacuum cleaner like noie levels at 60 dBA .... while all the dB charts put the vacuum cleaner at 70 dBA (typical for the 1970s), most of today's units are down closer to 60 .... right where the H100i is .... I find the noise from the 100i unbearable after about 55% CPU loading..... Watch .... er listen to the video here.
http://martinsliquidlab.org/2013/03/12/swiftech-h220-vs-corsair-h100i-noise-testing/
On top of that the new Radeon series is just about as loud as the 100i .... together, they can produce sound levels up close to 65dBA
The 750D is a fairly decent box for custom water cooling..... I'd suggest looking at this thread here for some ideas.
http://www.overclock.net/t/1430077/corsair-750d-owners-club
Otherwise....the H110 is quieter but again, these AIO water coolers really offer no significant thermal advantage over the better air coolers. A $75 Phanteks PH-TC14-PE has a slight thermal advantage over the Noctua shown below and is about 1/4 as load as the H100i
Other than a custom loop, the best I can suggest is:
1) Phanteks air cooler, H110 or step up to another level with something like the Swiftech kit.
2) Use only quiet mode on the 280x BIOS
3) If you have an Asus board, use AI Suite 3 to control fan speeds or use some other software equivalent such as SpeedFan. BIOS control will work but it's generally not as flexible as these options.
You could change fans on the H100i but it severely curtails thermal performance .... why pay $110 for a cooler and then spend $30-40 for quiet fans to make perform like a $35 - $50 air cooler.