I believe it is both. If you manually start it and wait a few minutes with the cab doors closed you will probably smell it. Most people get in, start it, and go, so no exhaust leak has time to get into the cab. Using the remote start and running for 10 minutes or so gives it time to vent into the cab. It must be a cold start too. So if you take it to the dealer, drop it off the night before, leave it outside, and have them remote or manual start it cold and idle for 10 minutes with the cab doors closed to replicate the smell.