Does anyone know why my car would vibrate in 3rd? 1st and 2nd are fine, then as soon as it goes into 3rd and i go above 60ks, the whole car starts to vibrate, and it gets worse the faster I go till I hit 4th, then it disappears (I 'tested' it up to 140 in 4th and there's no vibes). I think it is either the gearbox, or, at that speed, the ratio of flywheel rotations to driveshaft rotations is causing some kind of resonance.... ??????