'14, 2.7 auto PreRunner started with backfire?

Got a '14 Double Cab, PreRunner, 2.7 (I know the red headed step child of the 2nd gen) anyway, I've had the truck a month and 1/2 now and 3,300 miles. Got in this AM and cold started truck, even though it was still about 78 degrees at 9:30 am.

Turned key, and just before the motor fired, there was a fairly loud "pop" or backfire from the exhuast area after the motor turned over. Sounded like that pop you hear from a race car with straight pipes, as it downshifts into a turn.

Truck idled and drove perfectly normal from there on, just curious why it would have done this. Was kind of embarrassing to say the least. I've started the truck probably a dozen times since with no problem.

 

My 08 Prerunner w/ 2.7 & manual has done the same thing since new. Dealer told me it was normal. It has given me no trouble & has run great for 71k miles so far. It does it most mornings regardless of temperature.