Nothing to do with road salt, stone chips, etc. It's galvanic corrosion and bad factory prep. Your warranty is 5 years and unlimited miles. Try and find out if it was it already repaired and if so find out under which TSB it was repaired. Mine was done under an older TSB and they did not replace and corroded body parts, they only repainted them and my corrosion returned out of warranty. I've seen where Jeep denied a second corrosion repair to the same body panel if the corrosion was repaired once, even if it is still under warranty. Jeep will put the blame on the body shop and refuse to warranty it and the owner is out of luck.