Steering wheel locking while reversing?

When reversing while turning steering wheel to the right then into drive, my steering wheel completely locks, and it takes an extreme amount of for to unlock it. When applying this extreme amount of force while trying to turn steering wheel back straight, saddening I'll feel/hear a "pop" and steering wheel is loose again? What could this be and when does it only happen while reversing and turning to the right then back into drive?