Considering the job they do pushing air through a radiator the fans are not that noisy. If you want a quiet pc you don't want liquid cooling. A tower cooler from Be Quiet or Noctua are quiet and cool very well. Changing the fans on the h100i may get you a few decibels lower but you need to maintain a certain CFM and pressure rating to cool the CPU. Fans that meet those specs are not going to be very quiet. Throwing more money at a cooling method that's already expensive seems like a waste and in the end it's still not going to be quiet. Try making a fan profile that's a bit less aggressive at idle and moderate use that ramps up with hard gaming, but keep careful watch of temperatures.