A lot of the time when I flex my knees I get a cracking sound like when you crack your knuckles. Sometimes that cracking is accompanied by some pain when I flex. I did go to a doctor and he said that all he could see was some arthritis on the XRays and would need an MRI for better diagnosis. Since MRI are expensive I have held off. The other problem was that my knees used to hurt after playing but after using braces for both my knees while playing they dont really hurt as much any more. Apparently my knee cap moves around a lot and that causes irritation and pain and the braces keep it from moving. Still havent solved the problem of cracking while flexing. Was wondering if anyone has had that problem.