1996 Chevy Suburban problem with my vehicle

Hi my vehicle makes this loud clacking sound we have change alot of things on it the relay switches the battery and the starter we have change that twice and everytime w put a new starter it turs on but it makes a screeching sound then it gets messed up and it will turn on but it would make that clacking sound and we want to know what it could be and after a while that problem burns out the starter that's why we have changed the starter twice already can you help us