For sure pull the starter out and give it a good look. Might just be installed poorly as noted above. Check for dirt or grease inside, check for worn contacts.
- http://www.4crawler.com/4x4/CheapTricks/Starter.shtml

With a good cleaning and some minor repairs, it may be fine. If the drive gear or end bushing is badly worn, may be time for a high quality used, rebuilt or new starter.