Why does the hex nut make a sound? The answer is simple science. The hex nuts circle the inside of the balloon due to centripetal force. Centripetal force is the force that causes the hex nuts to move in a circular pattern.
The hex nut has 6 flat sides. The flat edges of the hex nut allow it to vibrate or bounce along the inside wall of the balloon. The screaming sound is created by the sides of the hex nut bouncing or vibrating along the sides of the balloon.