Turn your computer volume up, and listen for a high frequency cicada-like hum that increases in volume then drops off.  It can also be helpful to stop the video while playing to listen for the absence of the sound is sometimes more noticeable than the presence because it phases in and out.  Note the similarity between the phasing sound of the street transformers as compared to the interior fixtures and devices.

Sound evident at 0:10

Sound evident with peaks at 0:30 and again at 0:45

Sound evident throughout. Peaks at 0:35 and 0:55

Sound evident at 0:08

Sound evident at 0:18