Michelle - well, there are not one, not two, but THREE things wrong with it.
First problem - discovered via MRI and resolved via surgery was a plica - a band of connective tissue that isn't supposed to be there. Mine ran from the inside of my femur down across the side of my kneecap. That was what was snapping when going down stairs. The problem gets worse over time, but it wouldn't result in pain going UP stairs.
Second problem - knee tracking issue. Discovered via surgery, being resolved via physical therapy - my kneecap is supposed to move in a groove on my femur, and instead it moves over to the outside. This causes a different pop, in a different location, when my knee is straightened all the way, and when I lift my leg with it straight. It causes pain on the inside of my kneecap.
Third problem - scars in the bursa. This causes problems with kneeling and some "crunchiness".
Lannae - just hit goal! See link in my signature for details.
MadamePJ - thanks!