After 8500 miles (from new) I noticed a rumbling coming from the rear nearside tyre on my C250 AMG Line estate. The tyres are Continental 255/35R19Y run flats. When I took the car to my local tyre suppliers they noted that both rears were worn on the inside edges. Removing the wheels revealed a large bulge on the nearside tyre and when they were taken off of the rims and inspected internally it looked like they had been cut around the inner edge with large chuncks of rubber missing. Continental took the tyres back for inspection, have allowed a 40% rebate for unused tread but have not said what caused the premature failure. I have since, this week, heard of a B class on Continental run flats with exactly the same problem. Has anybody else had this experience or any ideas what caused it?