(For wood, rattan, leaves, bamboo, branches, etc.) to make a cracking, breaking, or snapping sound when acted upon.
That tree's branch made a cracking sound when I stepped on it.
What are you eating that's making a cracking sound?
To crack or break s.t. brittle (with a resultant cracking sound as when cracking one's knuckles, breaking sticks, etc.).
[The -an imp. focuses on removing s.t. by breaking it off or beneficiary. The -un imp. focuses on breaking s.t. off and using it.]
Why are you cracking your knuckles?
Break off some of the branches of that tree.