Broke my left patella in May. Now it always crunches a bit. The muscles, tendons and ligaments tend to get tight around it too frequently. I now have my own personal barometer as it changes with the weather. My therapist said that the crunching is most likely caused by an uneven surface on the backside of the patella. Perhaps you're starting to get some wear in there. Get it checked out and rexamine your bike fit and pedaling style.