Have you checked what's happening when it gets loud?
Is it because the Cooler is unable to handle the load and thus needs the Cooler fans on high?
Is the fan control on a very aggressive setting and doesn't actually need to be?
Is there insufficient airflow in your system that's caused the system to ramp the fans up causing the extra noise?
Because if any of those is true, grabbing new fans may not actually help your situation. As any fan running at (near) max speeds is going to be generating a fair bit of noise.