I have this smell too. Loren who runs Renntech told me what it was one time at one of our tech sessions. I can't recall exactly what he said though, but I just kind of shrugged it off as not being important then. I think he said it was either oil burning (I do have a little seeping oil but no drips) or from heavy use of the brakes. Why the brakes would give off a burnt rubber smell though I do not understand. I do notice this more after driving 100+ mph and then having to use the brakes heavily to slow down...
Kirk