Usually used in online video games when a player either gets killed, shot in the back, or cannot beat someone's score etc. The player yells in rage. This can be confused with rage quit but in rage growl, the player keeps on playing without quitting, but every time he/she gets mad, they yell in rage really loud such as "UGH!!!", "GRRRR", "AHHH". This can also be followed by phrases such as "Oh my God", "I hate this game", "I'm going to sell this game" etc.
*guy1 gets shot in the back*
Guy1: (Rage Growl --->) Ahhhhh!!!! I hate this game!
Guy2: Dude, calm down.