Ever since I have had my roadster (2-1/2 years) I have noticed a very slight but noticeable vibration felt through the steering wheel which lasts for about a mile at the most and then goes away. It will not manifest itself again until the car has sat in the garage overnight. Actually the feeling is more like a washboard effect than a vibration.

Road is blacktop. New tires, balance and alignment 2K ago. Car has 18K on the clock. My mechanic has gone through the whole suspension and found zip. He says everything is tight and in good shape. That includes the brakes and bearings. Says the car is brand new.

My guess. It is the tires. It dd it before with the old ones. I believe after sitting a day or two, the tires get a slight flat spot which take a 1/2 mile to a mile to get perfectly round again. I may be grasping at straws here but we are plumb out of ideas.

Anyone?