WARNING: This page is about a different car, the 2007 Kia Optima, 2007 Kia Magentis, 2006 Kia Optima, and 2006 Kia Magentis. However, it is still accessible from the selected car via links, so may be relevant.
Check the driveshaft boots for damage and deterioration.
Check the ball joints for wear and damage.
Check the splines for wear and damage.
Check the dynamic damper for cracks and wear.
Fig 1: Checking Driveshaft Boots For Damage And Deterioration