I walk down an alleyway next to a Subway every day on my way to work and all I can smell is some sour/yeasty/herby concoction that doesn't inspire me to want to go in. I think I've been in a Subway shop about 3 times in my 49-year life.
I worked at a Subway while in high school, and I agree the smell is not very inviting. Even the dough, once thawed, has a strange odor to it, though the biggest cause of that funky odor you smell is the bread proofer located beneath the oven. It circulates warm moist air around the bread to help it rise. The thing is, it's not cleaned regularly (at least it wasn't at three different stores I worked in), and when left unchecked mold forms on the bottom.
