Stay off of it for a while. You probably damaged a tendon pulley, which is a pretty classic crimping injury (is the hurt knuckle the first one out from the hand, on the middle or ring finger, perchance?). Although, it could be a ligament or maybe you smooshed some cartilege or some shit like that.
In any case, a crack or pop is usually not a good thing to be hearing from your finger (or any other joint, no?).
The usual suspects for recovery would include:
- not climbing on it for six to eight weeks or more (DFA has had finger injuries that took more like 3 months to heal)
- ice for a while, then heat (apparently alternating ice and heat work well)
- analgesics (e.g. aspirin) or anti-inflammatories (e.g. ibuprofen, naproxen sodium, or go the natural route and try bromelain)
- continue to be a good boy and not climb on it
- when you do eventually try climbing again, tape the finger above and below the hurt knuckle, and buddy-tape it to the adjacent finger (if it's ring-man, tape it to the middle, not the pinky--duh)
If the pain is severe or things seem abnormal with the joint, it may be worth seeing a doctor, as you may have ruptured the tendon pulley, which could require surgery (yay!).
Good luck; time to work on your pint curls for a spell.