I have noticed a problem with my LR3. When cruising down the highway at 70 mph I notice that when i gently accelerate to 75 the car has a noticeable (not violent) vibration from either the engine, transmission, or something, that lasts for a few seconds then goes away. It sort of feels like I am driving over ruts in the road. But if I push the accelerator down with authority as if to overtake someone there is no vibration. It only happens at speeds of around 70 mph. Otherwise the truck is a pure joy to own and drive. Any clues as to what this may be? Thanks.