The bug
Anvils glitch out and make noise when dropped on shulker; possibly because of the fix for MC-139493. Seems like the anvil switches between falling_entity and anvil rapidly.
Linked issues
Attachments
Comments 3
Another reproduction video https://www.reddit.com/r/Minecraft/comments/dt6w74/anvils_and_shulkers_dont_go_great_together/
slicedlime
Can't reproduce in 14b, it's either fixed already or I'll need more reproduction details.