Once the thermostat in the clutch senses the temp increasing, the viscous fluid in your fan clutch starts to drive the fan faster, similarly to the way a torque converter drives a transmission as it approaches lockup. The hotter it gets, the more significant the fan speed becomes and the main purpose the clutch holds on a very hot day is to limit fan speed by slipping as RPMs increase. When moving that much air, as the factory mech. fan and shroud is no slouch, you will have noise. I am running the flex a lite 175, but @ 2300 CFM of air capacity, that is clearly audible when running as well. Get a blower with straight cut gears and that should help your exhaust drown out the noise!
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