Coping with Post Runner's Knee/Popping?

So at the end of last summer I had an issue of runner's knee on my right leg - first time ever; It's healed up as far as I know - the doc says its in fantastic shape what with all my fitness routines but ever since then my knee has this urge to pop and not after doing 15-20 knee extensions does it go away (I am curious to see should that be of any concern??).

I'm quite confident my fitness levels are surpass the avg athlete, as far as I know if anything I'm fitter then ever - I can squat near double my weight no issue there which I know you need strong knees for

But... I think the damage was more physiological since this was the first time something had ever literally halted my momentum. I just don't feel like I'm what I use to be and sitting around probably isn't helping - I am a avid runner - I love it and can't see myself not doing it any length of time down the road; Prior to my injury, weekly I use to knock down 20-30 miles no problem - doing half a marathon literally every other week no problem. Now I am just unsure about doing anything more then 4 miles - yet I running as fast as ever. I'm just confused, is this just all in my head??