Shoulder pain

Im 18 and i’ve been weight training for 4 years and also started playing volleyball seriously 2 years ago.
In my beginnings in volleyball i’ve noticed that my shoulders pop in a weird way when raised more than 90 degrees and pulled back (imagine some sort of rotation from front to back but a little more on the sides) i have no idea what it is but my shoulders dont hurt until they pop and i then feel a very sharp pain. Anyone knows what it could be?