That happens to me as well when I do a certain exercise, the front of my thigh joint. Don't know why
It could be a variety of different things. The first thing it could be is your shoes. If there isn't proper support your body could be trying to compensate for how you walk. Does it hurt when it pops? Also, if your new to cardio pushing your body to a point it's not use to could cause the popping. Start slower and work you way up that.
Thank you so much did what you said tonight at my workout and it worked I didnt have any poping today thank you so much you have been a big help to me
What you can try is strengthening your erector spinae muscles (lower back muscles) by including a few back extensions into your workout routine. You can strengthen your hip area with a brisk warm up cardio, jog/bike preferably (low impact) then a good 5-10min of slow stretching of the hamstring, quadriceps, hip ADductor and hip ABductor muscles (do not bounce the stretch!). Then concentrate on doing some light resistance training on those muscle groups. Being limber and flexible is just as important as strength in the grand scheme of things.