How can you do preflight fan inspection when it's windy?
(YouTube) Reversers would slow down or stop the windmilling by blocking the majority of the bypass.

If repositioning the aircraft abeam the wind is not possible, then deploying the reversers does the trick. It's the same method used when starting a jet engine in strong tailwind.

Windmilling can be very fast. The clacking sound you hear is normal.

Jetliners don't have shaft brakes, but some turboprops do.