Swap the fans on the H100i to the opposite side of the radiator. Try using low noise adapters or setting fan profiles on the motherboard software to a low or silent profile. Monitor temperatures to see if the reduced fan speeds greatly affect operating temperatures.
The corsair SP quiet edition fans are great for the radiators or cases with restrictive airflow, but you should be able to just run the stock fans a bit lower to greatly reduce noise.
Another approach is to get the fans away from any grille / immediate obstruction. A lot of fan noise comes from the blades passing by the fan frame, case grille, radiator fins etc. Radiator manufacturers have many different dimensioned stand-off type surrounds for fans and radiators...