OK, so this has been bugging me for a while, and no-one seems to know exactly what it is or it's purpose.
On some vehicles (including the newer Rogue), I have noticed on the inside of the rear wheel arch, just above the tire at about the two o'clock position, there is a slight bulge/protrusion in the metal/plastic. I also saw it on my sons new Corolla that he just bought. It is also present on the latest Mazda MX-5, and I've seen it on the Alpha Stelvio as well.
So, what is it called, and what does it do?

https://www.theautochannel.com/news/202 ... n.4-lg.jpg

If I remember correctly (which I very well might not), its just a tiny bit of aero to keep the wind away from other joints/tail lights or something. Keeps whistling noises down.

Sounds plausible.
I look around now and see more and more vehicles with that little bump out/bulge on the rear wheel arch.
It must be working if more manufacturers are doing it.