Article Written by Laura E. guest writer.
The Corona phenomenon a violet glow, and hissing noise plus a production of ozone gas in an overhead transmission line is known as corona discharge.
The “HISS” of a Serpent No Less
Here is link to a very long and very technical article about what Corona discharge (C.D.) is. This article is a synopsis of the longer article.
Corona Discharges create purple light flashes and a hissing sound if your close to it.
What is Corona Discharge?