Have you been off the bike for a while, then just hopped on and the knee decided to act up? Is it "a lot" or just "a little"?

I've had my knee act up a bit, but I think it's overuse. Comes and goes, which makes me think I'm on the right track. Dialing back my power has helped (I was pounding away to keep up on group rides).

From what I've read, front of knee means seat too low; but then again, left side only means your body is trying to accommodate for something else. You could try reading Steve Hogg's stuff, it might help.