clicking knee

Over the past few days my left knee audibly clicks (not particularly loud, but it's still there!)when I am climbing stairs. Nothing obvious brought this on. There is no pain associated with the clicking and I have been able to continue my normal activities (gym, cycling etc) with no difficulties. Although this is admittedly trivial in comparison with major knee injuries, I am wondering if this is just "one of these things" that will likely disappear, or if I have any reason to have it looked at (i.e. what's causing it to click? -when I touch it as I climb stairs I can feel slight movement, but not extensive grinding). The source of my paranoia arises from a long lay-off from running (10 months) after extensive soft-tissue damage sustained in an accident to the same knee in Oct 2000, but I have since run a few half marathons and a marathon with no ill-effects. Any advice/ideas appreciated. I am a fit and active 25 yr old male (70kg).