With my new C70 I have a quite clear poltern, if I drive (with 20 – 30km, roof closed) over these flat (!) thresholds in the 30km zones. The noise does not come to me from the roof or the rear, but from the front axle. At one side (with only one wheel) overrun no such poltern is audible. With my two other vehicles (older T4 bus and 8 year old Seat Toledo) I always hear only a weak noise from the tires at the same road sleepers. Gruss: Peter (who is very satisfied with his new C70)