There isn't really just one Southern accent in the U.S.; there are quite a lot of differences in the way people speak in, say, the mountains of Tennessee, the coast of South Carolina, and the middle of Texas. It only sounds all the same to non-Southerners, in the same way that almost all English accents sound classy to most Americans. I have been able to tell that someone wasn't from a part of the South near where I grew up because they pronounced the word "oil" as "erl" rather than "awl."