A scanner must register the position of the scanning head very accurately. The motor that drives it is a "stepper motor" which advances to the next position by responding to an electrical pulse. The motion is a result of a series of thousands of pulses.
The higher the maximum resolution and the faster the scan speed the more pulses occur per second. Human hearing is at its highers response at about 400 Hertz so sounds at this frequency appear louder. Unfortunately modern scanners run somewhere in this range.