'03 Matrix What is this squeaking?

[wvgirl]

I have a 2003 Matrix XR.
I have noticed the past ewek that my car is squeaking....As soon as I turn it on it starts and the pitch changes when I apply the gas. Could this be the serpentine belt?? If not, what does it sould like to you?
Anyone replaced one before?? Can you do it without taking out the engine or should I just take it to the mechanic?
A little background...got it in May 2002 and it has 54,000 miles.

Thanks!