Answer:
It is not harmful, it is usually just your tendons rubbing over bony ridges in the joint. However, if there is pain you may have a possible injury, so be aware of that.
To stop this popping there are a few tips you should follow:
-strengthen your knee muscles by strengthening your leg muscles, such as the hamstrings and glutes, by squatting
-always warm up and stretch
-improve your hip and ankle mobility
-remove knots through soft tissue therapy using a foam roller or simply a tennis ball.
-Learn how to jump, the correct way is to land in a half squatting position
-Make sure to eat healthy! Fish oils help prevent inflammation and veggies and fruits improve connective tissue health
-Stop doing what hurts, take a break from the activities that cause your knee to pop