I've been experiencing a lot of clicking and popping sounds in my knees. It is more in left knee. I hear a click whenever I flex the knees.This has been happening since 3 months. I feel something is building up and I always have this urge to pop the knee And Sometimes I feel mild pain below knee cap and sometimes to the sides of knee cap. In the right leg also I feel warmth above my knee. I used to run long distances before but have not run since 6 months. There was no injury also that I recall.