Anterior knee discomfort - Causes?

Lately I have been getting a “discomfort” (it is like a very mild “burning” kind of sensation, just enough to be noticeable) in right knee, anterior and at the cap or perhaps on the inner side of the cap. Pain occurs only in this location. When I extend this knee, I can feel “clicking” but it is not painful. Interesting though that there is no clicking in left knee.

I cannot get a good run in because this knee thing flares up before my heart, lungs, and legs get tired. Going up and down stairs for long periods of time (i.e. 30 min+) also seem to be a trigger, as is squatting (not squatting down, but weight lifting squatting) and walking for long durations (>1hr) and hiking. I don’t even do squats anymore for fear that I may make this worse. Sitting is not a trigger. I do not feel any discomfort until several minutes into some form of exercise.

Has anyone experienced this before? I have a couple ideas what it might be, but not sure. Looking at the joint, maybe the cap is rubbing against the cartilage somehow?