2015 Sierra 1500 - Exhaust/Sulpher Smell - Loose exhaust component?

[TheWoodsman]

Wondering if anyone has experienced this issue or if there is something I should look at specifically under the hood...

 

I have a 2015 Sierra SLT 4x4 Crew Cab with 18,000 km on it, and recently when idling or stopped at a light etc. a strong sulphur smell comes out through the vents, and can also be smelt in the engine bay with the hood open but only intermittently.

 

I took it to the dealership where they ran a full check of all sensors, coolant system, battery and visually inspected the exhaust system for any holes and everything came back normal. Of course when they test drove the vehicle, the tech couldn't smell anything either. I picked it up, and the issue returned so I took the tech with me around the block where he could then faintly smell it as well. He replaced the cabin air filter and washed the bottom of the truck in case "burning road grime/dust" was to blame (which I highly doubt).

 

I crawled under the truck today armed with soapy water and couldn't find any leaks on my own and came up empty handed. I took a few pictures of where the headers connect to the down pipe, and the drivers side bolts/flange looked separated compared to the passenger side. I'll be taking the truck back to the dealer again in hopes of recreating the issue once more, but does anyone have an idea of what might be causing this? All the bolts on the headers look to be intact and snug as well.

 

Any insight would be greatly appreciated!

[HondaHawkGT]

With the engine cold, sstart it and have someone take a towel and cover up the tailpipe out back to restrict the exhaust. While they do that, try looking for an exhaust leak again. The leak should easier to spot then. Did the service tech scan the truck to see what the O2 sensors were reading?

[TheWoodsman]

Thanks for the suggestion, tried it this morning and couldn't detect anything unusual in the exhaust line. After googling the subject it sounded like transfer case fluid burning up can smell similar. Anyone have issues with their t-case?