From your follow-up description it sounds like your starter drive (or sometimes called Bendix) If you're handy with tools it's not a bad job and it'll save you a bundle. I would still take the starter to your local auto parts store to have it tested (usually free) because they load test it to make sure your starter isn't drawing too much power. The new starter runs in the $200 range - you can get a rebuilt for about 1/2 of that and if you replace just the bendix you'll be spending about $30. It all depends on how mech. inclined you feel.