Thump Thump sound when killing enemy soldiers

@sk1lld I think it might be similar. I'll need to see if I've got any videos handy where I get a headshot kill to compare them. It's a body-shot kill in that video though, as I've got the skull icon set to appear red for headshot kills.

Edit: There's one at around 8 seconds in this video: https://gamerdvr.com/gamer/elliotlh2678/video/189140575. To my ears, it sounds like a ricochet sort of sound, but I am pretty deaf nowadays. Also, you categorically do not see my dying to a smoke grenade thrown by a bot in this video...