Crepitus or crepitation is the noise heard during joint movements, such as cracking, grinding, popping, or snapping. You may have experienced crepitus in your joints, such as your knuckles, knees and neck.Here are some possible causes of these sounds.

Articular Pressure Changes.
Synovial joints have a joint capsule filled with synovial fluid. The volume and pressure within these joints may change during certain movements. As a result, gases within the synovial fluid can form tiny bubbles that eventually collapse again. These changes likely play a role in some joint-cracking sounds, such as when you purposely crack your neck or knuckles.

Bone-on-Bone Grinding.
As joints degenerate due to osteoarthritis, the protective cartilage wears down and adjacent bones might rub against each other. A similar process can occur when discs degenerate.When cushioning between bones wears away, the bone-on-bone grinding sounds are typically repeatable with each movement.

Ligament or Tendon Snapping Over Bone.
In some cases, ligaments or tendons make snapping sounds as they move around the bone or over each other. This can occur because our muscles and soft tissues are too tight, or because they become less elastic with age.

Neck crepitus is usually painless and rarely represents anything serious. However, if crepitus occurs with pain or other troubling symptoms, schedule a visit with your doctor.