A: There are a few variables that can affect noise level. The length of your duct run, the amount of bends in your duct run and the size of your restroom. A shorter dust run is better for performance and noise level. You want avoid having a bend or elbow right at the connection to the outlet or fan housing. If you used a reducer fitting between your bath fan outlet and your house ventilation duct, then the noise generated by your bath fan can be louder than normal. This can be adjusted by changing the diameter of your house ventilation duct to match the size of the fan outlet. Lastly as stated on the box, you want to match your square footage as close to CFM rating as possible. So, if you have an 80 sq. ft. bathroom you would want to have an 80 CFM fan, again this helps with performance and noise.