Having said this, at times the noise has no pathology behind it.
The various causes of knee locking
are torn medial meniscus, mis-aligned knee
cap, osteoarthritis, knee arthritis, torn lateral meniscus, osteochondritis dissecans, recurrent patella dislocation, chondromalacia patella, knee alignment problem, knee fragment or knee cartilage disorder. Hence you may need X-rays and MRIs of the knee to find the exact cause.