What Causes Burning Sensation In The Knees?

I am a fairly healthy 62 year old male living in San Diego, CA. I have occasional but intense burning pain in one knee (seems to be the outside portion of the knee and actually feels as if that area is on fire). I feel that I m a bit overweight at 6 0 and 210lb, considering my age. The pain usually lasts less than 2 minutes or so. It can be brought on with no apparent action on my part; but squatting/kneeling seems to trigger it, popping every time I stand up. Having never incurred a knee injury I m aware of, I wonder what could be a cause. No, I never played organized sports. Incidentally, having had 2 back surgeries I do know what REAL pain feels like. Thank you, Jim Rolstad