<<The sound is really going to come from your duct work and how many bends you have and whether your using insulation or not.>>

He hit the nail right on the head, most of these fans are built to be pretty quiet. I run a Vortex with a speed controller, don't have too much of a noise issue. If you do you can try various different things, like Racer said try using insulated ducting, or simply use *more* ducting to absorb the noise. Also hanging blankets in your grow room on the walls will greatly reduce the noise as blankets absorb a shit load of noise. Best of luck!