Crepitus is the term used to describe the sound and/or sensation of crunching as the knee joint bends back and forth.
Crepitus has many causes. An occasional pop or grinding sound can be normal, and
if it is not accompanied by pain or any other symptoms it is generally considered
harmless. Thus, if you do not have any other symptoms, no specific treatment is necessary.
If the noise is painful, however, this might indicate a knee problem such as osteoarthritis, meniscal injusy or patellar dysfunction and so on. If knee popping noises are painful and/or accompanied by swelling, it is advisable to see an orthopedic doctor.