The mostly likely possibility here is that this cracking and clicking is from a phenomenon known as cavitation within the joint fluid of your ankles or knees. Basically what this means is that, when you move the joint, small bubbles of air form with the joint fluid, which then coalesce and pop. When they pop they give off a cracking noise that is audible.
Cavitation is not a medical problem and doesn't usually require any specific treatment. However, it is important to have the issue checked out by your primary care doctor
when you get a chance, because there are other causes of cracking and clicking in the joints other than cavitation that are caused by joint problems. For example, degeneration of cartilage in the joint space might cause sounds that are very similar to cavitation. It is the case that most joint problems that cause clicking or cracking will have other symptoms, such as stiffness or pain in the joint, and the fact that you do not have any other symptoms is encouraging. Nevertheless have your regular doctor take a look just to make sure that there is nothing the matter.