In the german Motor-Talk forum there is the general believe that its the Tires. Although one member switched tires with no luck, others got new tires and don't have the problem any more.
You could try getting the tires swapped for a different vendor. The Tires that have problems seem to be Continental (ContiSportContact), Pirelli (especially the P7) and Goodyear. No one reported problems yet with Bridgestone.
Also: No Problems where reported with the variable sportsteering, adaptive dampening or a combination of those.
The base for this data is the reports of 32 Members of the german forum.