So this thread became relevant to my interests.
I, too, have the nasty burning smell. I assumed OP was talking about brakes, not the burning smell that comes from the rear passenger wheel well.
My best guess is that it's prop shaft grease, I keep mine juicy and I can see where it spatters on the exhaust. For a while I thought it was the wheel bearing going to hell, which it did, but the smell didn't go away after replacing it.
I managed to replicate it well by taking prop shaft grease and smearing it on my exhaust pipe (don't try this at home) and driving around.