I have noticed that the sound of my truck is really low for a couple of seconds after starting, then it sounds like something opens up and nothing but pure air is rushing out the exhaust. You can rev the motor up and get it to stop for short periods of time and it doesn't matter if the truck is hot or cold.

Is this normal for the 2015 or could there be something wrong with my powertrain?

 

Yes. The exhaust note changes depending on what different things the engine is managing. I don't know if those are turbo things or why it does it, but it's working correctly.

 

Good to know. It is a shame because it sounds real deep an throaty when it isn't doing that.

 

What you are hearing is the turbo doing its thing. VGT turbos make much better boost at low rpm, without sacrificing top-end power, compared to traditional turbos. The 6.0 and 6.4 do the same thing. At "smaller" turbo positions, they sound like an angry hair dryer. It's completely normal.