Pulsating knee? (or maybe throbbing)
 

I have this pulsating feeling in my right knee, as if some bubbles or something are passing through it, its above the right knee, on the left side, it feels as if it's not too deep under the skin. it's not painful, just awkward.

edit: I can even see it, I checked now, the pulsating is visible, skin is going up and down. I mean it occurs every few minutes or so.

Anyone knows what's happening there beneath the skin?

look, I even made a video for you: http://youtu.be/0IXy8s_aqI4 it happens by itself totally involuntary, every few minutes or so