 I purchased the 2017 Sonata in February; the car had 5 miles on it when I drove off the lot. At 150 miles, the engine became loud, especially upon starting up when cold. The engine chatters and vibrates and seemed extremely loud for a new car. The engine block also had corrosion spots on it. I took the car into the dealer and the service reps kept it overnight, told me they checked it out and there was nothing wrong, and they cleaned off the corrosion nad told me that was nothing to be concerned with. At around 300 miles, I discovered a defect in the passenger window and took the car back into the dealer. I again told them about the loud noise and that is did not sound normal; the engine knocks and certainly does not sound like a brand new car. They checked it out again and told me the noises are "normal" and that there is nothing wrong with the car. And of course they told me not to worry because if there is anything wrong, it's covered by the warranty. My car now has just now reached 3000 miles and I will be taking it in the for oil change. The engine seems to be louder; I was standing near another Sonata that was idling and one could not even hear it. My car is LOUD chattering, tinny sound, and when accelerating there is a groaning sound. It sounds like a a  very old car.  I drive very conservatively and at the speed limit, mostly in town, and the gas mileage I have gotten is not as advertised; the current "fuel economy" listed on the dash is 17.9. I got the car for its great gas mileage. Has anyone else had similar issues? I would like the dealer to replace the entire car. I don't want them to "repair" or replace the engine because it is a brand new car and should not have such issues, and if they start "repairing" it so early, it will certainly not be a new car.