Audi S5 vacuum noise on cold start
 

Hey there..

I have Audi S5 3.0T 2015 with around 16k miles and have a very strange problem. Every time the engine is cold and I start the car, I get higher revs (this part is normal), but when the revs go down (usually after a few seconds), it does this weird vacuum noise and then it stops.
I am not sure if this is a "feature" or if it might be a problem. I don't have any other problems with the car when driving.

Oil change, along with filters and the usual stuff was done at 11k miles.

- you can hear the noise in this video (around 0:25). The video is not mine, but my car does the same noise.

Any idea? I've tried searching with Google but couldn't come up with anything. Author of the video said that the problem disappeared on its own.