I suffered from knee injuries because of my volleyball days in secondary schools.
Before pregnancy, my knee would "crack" each time I squat, or bend my knees. It doesn't hurt but definitely felt a lot better after popping it.
After pregnancy, I guess the weight that I had on me while I was pregnant had aggrivated my knees further so even after popping my baby out, it still hurts.
What helps was to do half squats while using a chair (with a high backrest) to support yourself. I did this, a few at a time and went slower and slower as far as I dared.
Be careful not to lean over too much as you go up/down as this would imbalance you.
My knees are better now, and I still do it regularly. Squats help to keep you butt in shape