Help identifying this noise

[dmw319]

So, starting a few days ago I started getting this medium pitched flappy/farty noise on the initial acceleration. It only seems to happen when its a cold start and it only happens for a few seconds at most. If I feather the gas pedal really lightly, it doesn't seem to make the noise and after a couple minutes of driving it doesn't happen at all. I think it has to be drivetrain related, but can't seem to pinpoint the source with my ears. Everything under the truck and in the engine bay seems normal. Maybe something in the transmission (its an auto) ... any ideas?

Also, in the video I just happen to be turning, but it doesn't have anything to do with that.

https://youtu.be/ttkCLqhNw-8