I`ve run into some info that suggests that a pesky mystery knee issue I have sometimes is likely related to going too far over my head too soon, so
One method of diagnosing knee "issues" is to simply ride a spin bike with very little resistance at a relatively high RPM. (80+)
If you develop soreness on a spin bike with slight resistance then you should seek professional help if you ever expect to ride pain free. This of course, assumes you know your correct saddle height and pedal/foot/cleat placement.
Unfortunately, there are people who will never ride bicycles extensively without some discomfort.