Hi, thanks for writing to HCM.
From the given description, I feel that the popping out structure that is felt at the level of the malleolus
(ball of the joint) could be a subluxating peroneal tendon while moving the ankle.
Its definitely not dangerous at the same time not an issue to be neglected.
Consult an orthopedic surgeon for further workup and management .
Hope this information is helpful. Good day