Medical science is still trying to determine the exact cause of the cracking sound that comes from bones and joints. In almost every case, this sound is not cause for alarm, notes Johns Hopkins Department of Orthopaedic Surgery.
One theory suggests that as ligaments get tight from rapid movement, they make the noise. Another suggests that nitrogen bubbles trapped in the fluid around a joint make an audible sound when they are released during movement. Ligaments are also known to make a sound when they snap over or around a joint. According to Johns Hopkins Department of Orthopaedic Surgery, the only time to be concerned about the cracking sound is when it is followed by pain.