1998 Chevy camaro need help

I have a 1998 Chevy camaro 3.8 and my brother had thought the engine had froz n up. I bought a starter to see if that's the reason it wouldn't start.i changed the starter and when I started the cat it made a sort of like a fork stuck in the garage disposel a loud crunch y rattling nose.I took the starter back off to check the fly wheel looks OK but it still does it and it won't stay started please anybody that can help me email me a solution.thank you very much