Today, when I pulled away from a parking spot where I usually park, I had more battery charge than usual. So, I was able to go about a block and a half in EV. Instead of putting the windows up as soon as the first breeze came through, I left them down. The noise stopped within about 30 seconds or maybe less, though it could be that increased speed, other traffic noise, etc. made it seem to go away sooner.
One other thing to consider. I got my C-MAX with 113 miles on it already. My dealer informed me (weeks prior) that my C-MAX had been pulled for in-depth testing before shipping. I am going to imagine that Ford would have heard the noise when they performed this testing, and that they would have done something about it then, if it were a problem. So, I am not going to worry about it anymore. Besides, I got the 125,000 mile extended warranty. If the A/C fails, I will have a clean conscience about the issue.
I have my liftgate update scheduled for July. I'll bring it up with my service advisor, just to let the SA know everything I know, and to see what the dealership says by then. By that time, maybe dealers will have been given enough guidance from Ford about what, if anything, to do about the noise.
My C-MAX is running up to expectations. So, I am not too worried about the noise that I only hear with windows open, during the first minute of my startup.