What can cause the rear tires on a 2001 Mercedes SLK 320 to make noise?

What is your question?

The Mercedes Dealer said the noise was from the differential, but when I replace the two (2) rear tires the noise goes away for at least 10,000 miles and then returns. The Dealer checked alignment and said it was ok. More recently, the Dealer indicated that the suspension joints were worn and need replacement. Could it be these "worn" joints causing rear tire misalignment during driving conditions? The rear tires are wider than the front tires.