We just bought a 2013 ford escape and every morning when we turn on the ignition we hear a quick pop noise under the drivers side near the back (I think). Sometimes it happens if the car is sitting in a parking lot for a long time and then you start it. The same quick brief pop noise. Sounds like a popcorn pop. It happens when the car is cold. I cannot figure out if its something because the vehicle is running fine and its hard to prove to dealership. They said nothing to worry about because they could not hear it.
It might be a little bit of backfire I suppose. When cold the engine injects more gasoline, and some of that gas could be getting through to the exhaust and igniting in the exhaust pipe. Is there an exhaust pipe in the area you seem to hear the noise? I say this b/c I had a similar thing w/my Corolla, where I had been working on something and extra gas had gotten into the intake manifold, and when I started the car it sounded like firecrackers! For me just driving it a few minutes made the popping noise go away.
What you might be hearing is the purge valve for the EVAP system opening.
The carbon canister for the EVAP system is mounted near the gas tank along with the purge valve. When the ignition is turned on, the purge valve opens so when the engine is started the gasoline vapors are drawn from the carbon canister so they can be burned in the engine.
I bet if you look under the vehicle in that area you’ll find the carbon canister along with the purge valve. And with the engine cold,you turn on the ignition on you’ll find the noise coming from the canister purge valve.
Evap control solenoid is where the popping is coming from. See picture.