Sounds like your serpentine belt... could be going bad, or you may just need to tighten up your alternator.
The other possibility is a bearing in your waterpump or another part. Power steering? (if you see any green fluid... it's your water pump)
Either way, it's related to the belt, or something the belt goes around. Shouldnt cost more than $100 to fix. (plus labor if you take it to a mechanic)
If you feel brave go to AutoZone and by a Haynes book for the make and model of your car. When I purchase a vehicle thats the first thing I do. It will show you in the book how to fix ANYTHING on your vehicle. Best $25 you'll ever spend in your life.
A "Haynes" book is a do-it-yourself repair manual with lots of picture and illustrations. And there is not a vehicle in the world that they have not published a repair manual for. If you walk into any AutoZone there will be a rack of them by the front counter. If they happen to not have the one you need they can order one for you and have it within 24 hours.
If you take your time and are careful, there isnt anything you wont be able to fix (unless you dont have the proper tools) with the assistance of a Hayne's book.
Highly recommended for single ladies! Mechanics love to see single women walk in... $$$