This explains it. As one who have heard those sequence of sounds in a combat situation, it is something that you never, never forgets. It could not be anything else. Well done, Marines.
I’ve never been in the military, let alone been a Marine; though my father was. I am, however, the owner of an AK pattern weapon and even I know that there’s only one thing in the world that makes a ‘Tok-SHRACK-SHRACK’ noise. If you’re *not* at the range or a gun shop and you hear that noise, bad s**t is about to happen.