I'm surprised at the 12V fan (72p). At 12V it's as quiet as any fan I've seen with the same airflow. At 5V, it's barely audible, and still moves a decent amount of air. At 3.3V, it's inaudible (20cm from fan) and creates a reasonable draft.
There is no "clicking" or electronic noise from the rotor at low speeds like there is on many fans.