2002 Other Mercedes Benz Models bumps

My e430 awd bangs and rattles over bumps. It seems as if the tires are skipping over minor bumps and I feel the steering is unstable when entring bumpy turns and off ramps. The ball joints have been replaced and the dealer states that the front struts are ok. The tires are new ( six months) but are wearing on the front outsides slightly. The steering wheel is off center. Can this be an alignment or tire issue? I have adjusted the tire pressure accordingly.