The features of the Noctua NF-A4x20 5V PWM at a glance This makes the NF-A4x20 surprisingly quiet, even at close range. The NF-A4x20 is equipped with the further optimized second generation of Noctua's proven SSO bearing system.
Generally a good experience as a cooling fan. However , since it was bought to cool a Jetson Nano (suggested on the Nano info pages) the fact that the mounting screws don't fit the Nano's heat sink is a very negative thing.