I received them today! Installed...the quality of these Noctua fans is about 100 times better than the Corsairs. Even the packaging is beautiful!
The sound levels have decreased significantly compared to the Corsairs - although I have used the low noise adaptor with the Noctuas my max tamps whilst stress testing have only gone up by 3C! Definitely recommended!
I had exactly the same thing with mine. The Corsair fans supplied with the H110i GT are absolute junk. I have Phanteks PWM fans as well and they are good but probably not quite as awesome as the Noctuas! The rattling and noise are a thing of the past!
Also with regards the above post, Noctua recommend the NF-A14 for radiators and considering how much quieter they are the loss in performance is minimal. With the H110i the rad is so big, unless you are pushing the limits of your CPU I wouldn't bother going from max CFM from a fan but rather something quiet.
EDIT - I have just removed the low noise adaptor...as actually with the PWM control and custom curve I can limit the speed of the fans up to a certain temp in CL and allow them to speed up to max when the CPU is hotting up!