Almost right.
The clacking noise is made by the mid span snubbers hitting each other as the fan blade goes over top dead centre.
If you look about half way along the span of a CFM56 fan blade you will see them. They are there to ensure the blades remain rigid especially in the event of a bird strike.
More modern engines such as the IAE V2500 or RR Trent have more advanced wide chord fan designs that do not need them. They are virtually silent when windmilling.
