WARNING: This page is about a different car, the 2006 Buick LaCrosse and 2006 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Inspecting Engine Flywheel
Courtesy of GENERAL MOTORS CORP.
Clean the flywheel.
Inspect the engine flywheel for damage and cracks.
Inspect the engine flywheel ring gear for damaged teeth.