Just found out why there's sometimes a buzzing sound ... The device is regulating the power output based on the frequency of the electrical wave. Most modern mods regulate power output by the amplitude. How often the electric pulses come rather than the size of the pulses. FM & AM but with waves of electricity rather than radio waves. Okay, i really don't understand all that, and probably explained it poorly, but that's why there's a buzzing at certain wattage settings; you're hearing stray electricity flowing. It's a small amount and so not dangerous.