How much noise should be expected from the motor while it is running?

Some high frequency noise is common when closing feedback loops with permanent magnet synchronous brushless motors. Factors that influence how much noise is present are: encoder resolution, whether or not filtering is used, PID gains, and the fidelity of drive chips (example: ADC resolution, meaning 12 bits over full scale current or 18 bits over full scale current). Adjustment of any of these can significantly reduce audible noise coming from a motor.