The noise you hear is more than likely coming from the gas cap. The gasoline vapors in the gas tank expand inside the tank, especially in the heat. Sun on the tank and heat from the engine makes it worse. The gas cap has a small vent controlled by a diaphragm which allows excess pressure to escape, thus the whine/ whistle/ whimper/fart / beep whatever you want to call it.
You can hear the tank whistle at the end of the video.