Why would my ankle "pop"? I've developed a weird "pop" in one ankle when I walk.

Ligamentous Laxity. The ankle should be evaluated for prior ligamentous tear, synovial cyst, ligamentous laxity, lesion of the talar dome, tendon lesion.
This . This is a tough one to answer without examining you. The first thing i can say is that if it doesn't hurt, try not to worry about it. Pain is the best indicator we have to tell us that some is wrong, and that we should pay attention to it. Snapping around the ankle could be due to a tendon slipping over another on top of your foot as you range your ankle. If you have had a previous injury or surgery on your ankle, there could be some scar tissue that is rubbing over a bony prominence and making a snapping sound. One thing to try is to not make it pop intentionally if you can. Often times, these are due to inflammed soft tissues, and making it pop to demonstrate to others only worsens that inflammation, and thus leads to more popping. Again though, the most important point i will stress is that not everything has a defineable cause, or at least one worth investigating, and this is particularly true when the you are not having pain associated with this.