What causes knees and ankles to pop when walking?

Ankle Popping: Popping can range from mal-alignment of the tendons not tracking right to arthritis. Depending on the issue, orthotics from a podiatrist can be quite helpful. Even if currently not painful, you should see a podiatrist as these tend to become progressively worse over time. Early intervention is the the key to prevention.

If this popping is : Painless and been going on for years and sounds like you're cracking your knuckles, chances are it's just a little gas bubble being popped, much like bubble wrap, and is harmless. A tendon slipping off a bone shelf can do this too, but it's usually painful, and it's hard to imagine something like that affecting both knees and both ankles. If you have no pain or swelling, relax!