AC will create a tone at the frequency the machine is set for. The arc directly vibrates the air like a Tesla coil. Also the arc length has an effect as that causes the voltage to change. A long arc length will be louder. In theory you could modulate your weld frequency with music and the arc would play a tune while you're welding. Not very practical, better to use hearing protection when doing AC TIG , especially over an extended time. You will get a similar effect when using hi frequency pulse settings on DC.