2005 Buick Century Squeeking noise

My mother owns a 2005 Buck Century. I am not sure what the engine size is, but i believe it is 4cyl. When starting up her car it makes that squeeking/squeeling sound. I was told it was a fan belt, but i am skeptical. When accelerating it tends to seem a little louder, but after a certain period of driving or speed, it goes away. Please help us, so she doesnt get ripped off by a swindling mechanic. Thank You.