I have a 2007 Sirion with the 1.0 engine. It has developed a vibration when the speed is between about 60 and 70 mph, but is smooth above and below this speed range. You can feel a sort of droning buzz through your feet.

It's not related to engine rpm, in fact you can de-clutch and it makes no difference. I've swapped the tyres diagonally but it makes no difference. My Daihatsu dealer can't find anything wrong. Any thoughts?

Thanks
Dave