Popping or crunching sound in knee
can be due to
arthritis (it can be rheumatoid arthritis too). It can also be due to
medial or lateral meniscus injury or patellar injury (caused by active sports, dancing, exercising or accidental). Another possibility is Chondromalacia patella in which the knee cap keeps rubbing against the underlying cartilage of femur (corrected by braces, taping, non-steroidal anti-inflammatory, physiotherapy or surgery).