Here's Ralph explaining it:

Experimenting with my GoPro3... attempting to capture the HellCat's incredible baritone fury...then a CTSV on Slicks got into my crosshairs! Was a fun couple of laps chasing him down. The CTSV driver overcooked a few corners (admittedly) as he was driving in his mirrors as the Cat closed in! The highlight of this video is not the little bit of track action but THAT engine note...IMHO it has gotta to be one of the best sounding engines available on the market today. Hats off to the SRT engineering, power train, exhaust and integration team. The Hellcat simply works as a system. Loads of character, grit and pace!