You can't hear the engine running because the car sets off on its electric motors. The petrol engine does not start running until the car reaches about 10mph or the batteries need regenerating. The whole point is to reduce emissions at low speeds. You do hear the engine start up later in the journey, though it's still fairly quite. The RX400h is actually more effective than any diesel SUV the same size. Gives you near V8 performance. Yet about 33mpg, and you won't get that from a diesel X5. You don’t have a good reason to reject it.