Strange sound

It's been pretty cold here lately (A NoCal cold - in the low 40s! ). When I first take the 'stang out, I am getting a strange sound when the rpm's are below 3k. Kinda sounds like blowing on the top of an empty bottle, ya know? Anyway, it only lasts for a couple of minutes, and then it is completely gone!

Other than that, the car is completely normal - same power, same handling, same everything!

Since I'm primarily solo, I can't really record it. Anybody else have this? Any ideas what it might be?

I think it may be your A/C. I noticed this on my car, a faint "whining" kinda like blowing over the top of an opened bottle, shifting to second it would get more faint, 3rd it was almost gone, then couldn't hear it when up to speed.
Had to take mine in and have the whole unit replaced (compressor and evaporator is what I was told). Took 2 weeks but didn't cost anything....Service manager at ford said this is an issue and the 15/16 are starting to come in frequently. Anyways.... Good luck!

Thanks! I'll have them check it out!

Normal.