An effective method is to take a stick, an inch or two in diameter, wrap it in a wet towel, and snap it swiftly. Do not wrap it too much, or the sound will be muffled.
Cracking knuckles sound like cracking knuckles
Air-crafts make a sonic boom known as a "boom'sound or 'whip cracking' (cracking) sound.
knucklephobia
shooting a gun would probably scare him
It makes like a cracking noise
trees make crack sound when they are lacking water or about to break.
The sound is caused by static electricity.
The Slap Stick
Animals use sound to communicate and/or scare away predators.
Break or cause to break suddenly and completely, typically with a sharp cracking sound.Emit a sudden, sharp cracking sound
Thunder is the sound of the lightening cracking the sound barrier as it is breaking through the earths atmosphere.
When you crack your knuckles, your bones are rubbing together. That's what makes the cracking sound. It used to be beleived that cracking your knuckles caused arthridis, but that been prooved untrue.