rear window shattered while on entrance ramp to highway. Can't say what caused this --INFINITI and dealer claim it must have been a pebble or small piece of rock that was thrown up from car in front of me and land on back window. I cant understand how that is possible to do so much damage --considering possible velocity and trajectory. Car is months old and Infiniti is not being helpful. I want this on record in case this is a problem-after all it is a new car.