I as well have this "the click and the slight numb pain" i originally got this from football
Though i do not notice the pain or the click when squatting with weight because I'm to focused on keeping proper form and what not.
I researched and found out what caused it and what exactly it is quite some time back however i did not retain the information
It does not affect me in the least in every day life or lifting for that matter HOWEVER
IF i sit Indian style then try to get out of it to quickly or exert to much force downward i can actually "Lock" my left knee in place and then its a slow process of "un locking" it, so i just cant sit Indian style without being careful.