Faint backfire sound when starting

About 75% of the time when I start my 2014 2.7l base 2wd, 5 speed manual with 67,000 miles, I hear a very faint single backfire noise coming from what seems like the rear exhaust area. Not very loud at all and the truck still runs and drives great and not throwing any codes. Gas mileage is the same as it always has been. After I start and hear it, I don't hear it again until the next start (unless its one of the 25% of the time when it doesn't happen). Anybody know what this is? I'm not super concerned because everything else is great with this truck.

 

I too would like to know,
I have the same engine, and similar backfire /pop on occasion