I may be a bit late in this thread, but I hope not. I have had knee problems in the past, and the sole cause was not warming up properly. I used to try to go too fast too early and my knees just weren't ready for it.

Now I generally pedal easier in the really early stages of a ride, and generally my legs will tell me when they're ready for me to increase the intensity a little. Now I don't have knee problems anymore.