Boil the macaroni in a 2 quart saucepan in plenty of water until tender, about 7 minutes. Drain. In a medium saucepan, mix cheese and butter. Stir until the cheese melts. In a slow cooker or crock pot, combine cheese/buttermixture and add the eggs, sour cream, soup, salt, milk, mustard and pepper and stir well. Then add drained macaroni and stir again. Set the crock pot on low setting and cook for 3 hours, stirring occasionally.