Causes of Knee Popping or Snapping
Knee popping, snapping, cracking, or crunching noises are usually harmless and may simply be the consequence of aging joints. But they could also be an indication of a serious injury, such as a torn meniscus, or an early sign of knee arthritis. This is especially true if the noises are accompanied by pain or the loss of joint mobility.
Source: Verywell Health