Mysterious two tone alert sound/beep on highway? [2012]

[Twotonebeep]

I borrowed my father in laws car and while driving on the highway it gave a two tone alert (two short tones in quick succession within 1second). No visible signals on the dashboard and we had the center screen off. Later on it again gave the alert, then two times with a minute in between. On the road back it happened 3 times in a minute.

My father in law doesn't know either. He thinks it has to do with the location. Speedcontrol detection? Lane departure detection?

Year of build is 2012. The tone doesn't sound like a warning, rather an alert. It's two tones in quick succession: beep-beep.

What can it be? 

[Briano]

Sounds like speed camera alert to me.

[JiiN]

Propably speed camera alert. I think it can be set off at navi's settings.