So, the last two days here were my first with my 19 Expy in the snow. And the first time I really played with 4A (don't have 4L, and this is my 2nd ecoboost v6 motor). After putting it in 4A I noticed what sounded like a turbo spooling up while accelerating, at any rate. I tried various levels of throttle pressure. Even with minimal throttle pressure, watching the traction gauge, and not seeing any drive being given to the front wheels, I hear it. When switching back to 2A, and doing the same exact tests the noise was not there. I tried the same thing today, on clear/dry roads, with the same results. Could these be the turbos I am hearing? But only in 4A? Why would I hear them in 4A but not 2A? Or could this be the mechanics of 4A, with a front differential being engaged and actually spinning? And I am therefore hearing that spooling/spinning/whirling noise? But if so, is it completely OK to leave in 4A full-time, say for a snowy 3 hour highway drive? Anyone else notice the sound? I wouldn't say the noise is loud, but I notice it. If I were to leave it with the dealer, and told them about it, they would probably test it and say "what noise?" Then I'd have to ride with them and point out the noise, at which point they would probably pick up on it.