There could be several reasons why your fan is generating more noise than expected.
First, please perform a visual inspection and make sure nothing is interfering with the fan's operation. In some cases, debris from the ductwork may enter the fan and cause additional noise.
Second, remove the fan from the vent and place it on a table or other flat surface. Turn it on and compare the noise level to what you hear when the device is installed in the vent. The noise level should be very similar. If the fan is significantly louder when installed, the vent itself may be contributing to the noise.
Please note that the 3x10 models naturally produce more noise than our standard 4x10 models. Because the 3x10 units use smaller fans, they must operate at higher RPMs to generate sufficient airflow, which results in a higher noise level.