The major bones of your leg, the femur and tibia, may be out of alignment at the knee joint.
rob1880 mentioned seeing a chiropractor, and I agree, a good chiropractor can usually fix this in a few seconds, if this is the problem.
Plyometrics and basketball are both high impact on the joints. When you do plyometrics, are they concentric or eccentric?
I would also be very careful to check your technique on all leg exercises in the weight room, any breaks in form, can cause huge problems over time.