I just finished my third week of a ten week bootcamp and kickboxing workout program. I've had a tender right knee since my days of sports, but I just noticed today that when I flex my left knee it has a really distinct crunching sound that is lasting and sustained. In other words, not just one "pop" but a sustained crunching sound all through the flex. Here's the kicker: the knee is not sore and I feel no pain in it at all.

Any ideas or things that I should watch for?