There are some "rough" duty H4 lamps that have additional support of the filiament inside...next one you replace, check for it...! And yes, you should also check for bad connection, if the light is flickering along with the vibration, the life of the filiament will also be shortened because of fatigue and rapid heating and cooling. Also there is an opening to allow trapped hot air to escape out the shell if memory serves...make sure it is open. :coffee
