A screeching noise can be caused by a variety of things. If if it is a consistent whiny screech, or if you hear it while braking, it might indicate that it's time to replace your brake pads. If you hear it while accelerating, it could mean that your engine belts are slipping. DIfferent sounds can indicate a variety of engine problems as well.
Either way, it's best that you take your car into a reliable shop to have them evaluate the sound.
For additional assistance, please find an AskPatty Certified Repair Shop at http://www.askpatty.com/search/?type=all&m=30&q=&keyword= and they can help you diagnose and repair the problem.