Belt(?) Noise when slightly accelerating?
 

I noticed today with the windows rolled down, there's an odd sound coming from I guess the engine compartment. When I want to accelerate, pressing the gas pedal slightly makes something (maybe a belt?) make this repeating noise for a short period of time, a few seconds. I know that's vague, it's not a high-pitched continuous whine, it goes away after you accelerate past around 2500rpm. It only makes the noise when starting to accelerate. Any ideas? It sounds like immediatly when the guy in this vid touches the throttle, http://www.youtube.com/watch?v=PuAU8tTZnVg