1. The sound you hear after being punched repeatedly. This is usually accomplished by a bully of some sort.
2. The sound of a habitual knuckle-cracker, especially one who is capable of cracking many knuckles at once.
"Oh man, Jimmy's probably hearing a knuckle symphony right now! Lets call an ambulance."
"Hey, man, thanks for the knuckle symphony right there. Really appreciate it."