Why We Hear Humming Sound When Standing Below High Tension Powerline?

Have you ever heard that buzzing sound while standing below high tension powerline? Hi folks it's Aditya and today ask the question on steemit why do hear humming sound when standing below powerline.

Transformers are a different story, but with just high-voltage (generally >350kV) wires the standard explanation is corona discharge.
In the air occasionally some gas molecules will become ionized. This means that the molecule gains or loses and electron. This can happen through chemical reactions, but it's generally more likely that UV light knock an electron off. An electrical field doesn't really affect uncharged molecules, but it does affect ions. The positively charged ions are relatively heavy, so move slowly, but the free electrons are very light so they get pushed away very quickly. These fast moving electrons bump other molecules and can knock more electrons free. In addition to moving ions, this can cause a slight glow (when an electron recombines with a positive ion), and heats the air which causes noise.
A negatively charged wire will attract positively charged ions, are push away the free electrons (or any negative charged ions), while a positively charged wire will do the opposite. In a power line carrying AC current, the charge on the wire alternates between positive and negative (with some time in between where it isn't enough charge to matter). The result is that the air gets briefly heated 120 times per second, which makes a hum.
If the wire is smaller, then the electric field near the wire is stronger, so one of the reasons high voltage wires are as large as they are is to reduce this effect.