A popping joint is normally no problem if its not causing pain, if it is causing pain you need to have it looked at.

The construction of the knee joint is pretty complex its actually the most complex joint in the human body http://academic.wsc.edu/faculty/jatodd1/35 1/knee.jpg you could have worn away some cartilage, or torn a ligament, for the moment I would try keeping off you feet and iceing where you are getting pain then see a doctor ASAP.

When you turn on your feet you should try to lift your leg and turn you should not spin on your feet as this puts unneeded stress on the knee joint and can tear ligaments.

Im not a doctor, but have had a Lateral collateral ligament tear and it took forver to heal, I did have to use a compression bandage also but I would advise you not too untill you have spoken to a doctor, I think it took 6 months for it to fully sort itself out, I'm a pretty active guy so I did not really give it a chance :O).

Eddy