Electronic throttle car, when the ignition switch is turned on, how can there be noise in the cabin? What is it and why?

For all models with electronic throttle, when you turn on the ignition switch, the whole system starts to work. At this time, the engine computer sends an electrical signal to the electronic throttle control unit, so that its operation is initially set, and finally it returns to the best state to ensure the normal idle intake of the engine. The sound you hear is the sound of the throttle motor.