This is a very bassy kick sound done entirely using your throat. Many beatboxers put a microphone against their throat to emphasise this fact - it's very effective, and generally a real crowd pleaser. It's not particularly hard to do, but putting it into a beat can be tricky.

To make the sound

1 - Build up some pressure in your throat
2 - Let the air through your windpipe keeping it nice and tight
3 - It should sound like a gulping sound

This sound has many different names including, but not limited to, the 808 kick, techno kick, techno swallow, throat kick, and techno bass.

Peace, love, and throbbing bass

-FT