I've recently accquired an st170 it has the xenons but I prefer the black non xenon headlights.are the original xenon units worth much money second hand? I've heard they are rare to come across? Also when the car is ticking over you can hear a slight rattle 2 or 3 times its like somes tapping a hammer on the side of the engine? Is this the dual mass on its way out?? It starts and drives fine? How long do they usually last from making a noise to self destruct? What will happen if it fails? Non starter and no gears? Thanks