BowtieBandit - I finally got my Yukon back to the dealership and got the same answer to my complaint - they all do that. I presented them with the printout from this forum and they had to confer with GM on what to do. They had me bring the car in and did the 'de-carbon' routine and replaced one spark plug. That, to the surprise of the dealer, made the noise go away.
I forgot to mention that this particular Yukon is a bi-fuel vehicle. I have a propane conversion on it and run on propane about 90% of the time. I am surprised that there is a carbon buildup running on propane.