I think a lot of it has to do with the tires. I went through 3 sets of tires on my Sonata, each a different brand or series of tire, and they all had different noise characteristics. The last set, Goodyear Assurance Touring, were the quietest by far. My 2015 Elantra, which I just bought this week, has some Hankook tires (stock?) and they're not too bad. I hear rolling noise a bit, more than my Sonata of course, but not so much from bumps. I've had small cars in the past and I just think they are more prone to let noise into the cabin by their nature. If you want quiet, you have to step up to larger and more luxurious cars, IMHO.