Boom-boom

What's this oddball expression mean? Where's it from?

Roughly translated, hooray. It sprung up within the last 5 to 7 years among young people. Source?

They were saying something like it in the movie "Black Hawk Down."

From a submission to UrbanDictionary.com --
booya "boo yaw"
1. A threatening phrase derived from gang terminology for the sound a shotgun makes when fired. 2. An exclamation.
"This (bleep) was creepin' tryin' to gaffle my whip, but I snuck out the crib, cocked back, and BOOYA, splattered that fool's brains all over the driveway!" "Booya grandma, booya!"

boo-ya adj. [1990s] (W.I./UK/US Black teen) totally wonderful, incredibly fine. [? hip-hop group the _Boo-Ya Tribe_]
booya!/booyah! excl. [1980s+] 1 (US campus) a term used to indicate suddenness or surprise (cf. BANG; WHAM!) 2 (US Black gang) an echoic term used to imitate the sound of a shotgun being fired (cf. BOOYAKA!) [SE excl. _boo!_ + _yah_]
booyaka! excl. [1980s+] (W.I./UK Black teen) an excl. of delight, pleasure, made by using the mouth to simulate gun shots fired in celebration or appreciation of something (cf. BOOYA!; PRAM! PRAM!)
From Cassell's Dictionary of Slang by Jonathon Green