After the gun has a couple thousand rounds through it, it should go away. This is usually caused by the disconnector catching in the hole that allows access to one of the optic mounting screws. The disconnector tension is caused by the trigger bar spring, and the sharp edges on the hole, once broken in, it should go away, or atleast mostly go away.
all that said, it doesn’t effect function of the gun, only happens when hand racking it gently...