If the popping noise is only occasional, it is possible that this is simply due to cavitation within the hip joint, which refers to the generation of small air bubbles that occur when the joint is moved quickly. These air bubbles produce a popping sound. This process is totally benign and doesn't need to be worried about (it is analogous to cracking your knuckles).
On the other hand, if the popping sound is more regularly associated with bending the hip, and if there is any discomfort along with it, then you may be suffering from snapping hip syndrome. This is most commonly caused by the vibration of tight tendons and connective tissue moving over bones. Usually it is the iliotibial band which is the cause, which is a bundle of tissue running up and down the outer side of the hip. This form of snapping hip syndrome can usually be effectively treated by stretching exercises and proper shoe wear to minimize over pronation. It is possible to get snapping hip syndrome after a more serious injury
to the hip, such as a hip subluxation, but it is more commonly just related to tight muscle and tendon tissue. Talk to your primary care doctor
or a sports medicine doctor
for more information.