Ok Im a flight attendant and on my feet for each flight. My knee would hurt if I move a certain way as if the joint is popping and like i moved the wrong way. at that point it hurts but then the pain will go away and come back if i move or bend as if sitting down.
You have not mentioned your age. I f you are young age and having this sort of problem it could be some calcification in the soft tissue(synovial) in the joint or some crystal deposition like Uric acid. If you have crossed 40, it could be early degenerative Osteoarthritis. You need evaluation with Orthopedic surgeon.