It's an internet meme, starting with the children's anime, Dragonball Z. I'm going to do some guesswork here, as I don't actually watch it. At any rate, I believe everyone has a "power level", which changes based on how psyched up they are. Or something. So at some point the hero, probably Goku, gets really pumped.
"Vegeta! What does the scouter say about his power level?"
Vegeta then tears the little device off his head (it's one of those robotic eye lens things) and smashes it for no apparent reason.
"IT'S OVER NINE THOUSAAAAAAAAAAND!"
"WHAT, nine thousand!?!"
Someone recorded that, repeated it a gajillion times, played with the speed of it and uploaded it to Youtube. Hilarity ensues.
4chan decided it was awesome and spread it all over the place. Instant win. Furthermore, it features in "Yu-gi-oh: The Abridged Series". One card gets more than 9,000 attack points, and so they use that sound clip, placing it over the two other guys talking.