When I perform side-lying leg lifts my left knee (and maybe even hip) seem to move out of place and go back in. It feels like little pops, but they re not really audible popping noises, I can just feel the knee pop or move out of place for a moment. Not sure if it s related, but since 09/04/14, my left knee has also been hurting off and on (especially after exercise). It doesn t hurt to walk normally, but speed walking does aggravate it & cause more pain. I ve also noticed that while commuting to work it starts to bother me &/or hurt & I feel like I need to extend & stretch out my left leg/knee. Extending my left knee straight out in front of me while seated causes grinding/popping/cracking, but it is not always painful. How can I fix this and continue to exercise (cardio, walking, jogging, ballet & ballet-inspired workouts, various dance workouts, etc.) Thanks in advance, Sonia