This sound is called “crepitus

,” which is defined as “joint noise.” Popping knees are not unusual. It happens when carbon dioxide builds up in the joint's synovial fluid and is released as a gas bubble that bursts when the joint adjusts rapidly. It is the same process that causes knuckles to crack.

Is it bad if your knee is cracking?

Popping and cracking sounds usually aren't signs that something's wrong. “A lot of joints crack and the knees are a really common joint to crack,” says David McAllister, MD, director of the UCLA's Sports Medicine Program. “Most people have knees that crack when they squat down or go through the full arc of motion.

Why is my knee cracking a lot?

If the thigh muscle (quadriceps) is too tight, it can pull the kneecap and affect its free gliding movement, generating a knee crack. If the various soft tissues such as cartilage or meniscus have degenerated, resulting in loss of smooth cover of the knee joint, and leading to knee cracks during various activities.