[that_red_c10]

Ok so I tried starting my truck for today, and it would crank but wouldn't start, then after awhile it stopped cranking and started making a really loud scraping noise like a train scraping against its tracks, but louder. I took a look under the hood and every time we tried starting it, the alternator would move maybe a centimeter then jolt back. I'm really worried because I don't know what's wrong and hoping I don't have to buy something very expensive. Thanks everyone!