@RavenNL This Effect can appear when a Ambulance,Policecar,Firetruck passing by in front of your camera or you are moving the camera while the cars driving by.
You can hear this "High or Low Pitch" Effects even at the Vanilla Game - unfortunately, because the Soundengine of the Game is very "basic".The Soundfiles are all original and untouched, you can find it in the Steam Workshop Folder.

@0xyl0n - #K0L3M Brody# the ambulance sound isn't correct. it plays in slomo

it´s just a sound Demo from the german sound pack to get an impression

I have read it, but the audio in the video is clearly form Germany, even though it says that the stations and sirens will be country specific. So is the audio in the video wrong?

read the Country-specific changes above

there is no difference between this and the german pack?