Well, as it turns out, it wasn't the gas tank at all. Even though it was scraped, that must have been a previous driver going over speed bumps too fast. Turns out the 245/50s were not only rubbing the sway bar in the front, they were also scraping something in the wheel wells in the back.
Took it back to the dealer and he gave me 4 new tires - 225/55 R16s. No more rubbing in front or scraping in back.
Color me happy!
