What were you doing when this showed up?
Have you looked at anything up/down stream of the knee?
The quad may be an impacting factor.
A couple places to start:
Pro Episode # 52 – Pro user Request Friday: Couch Stretch Feel Weird? It’s a Diagnostic Tool too.
Voodoo Band Your Patella Femoral Pain
Wonky, Beat Up Joint? Feed That Thing Good Mechanics and Some Slack
Pro Episode # 31 – User Request Friday – Live from The Games: Patellar Tendonitis
Episode 344: Compression Tack and Floss–The Knee