Loud ding/beep noise similar to physical presence
 

There is a loud, and interrupting "ding" noise, similar to the noise you hear when you're about to hit something while parallel parking that happens every time I drive by this section of above-ground light train track (unfortunately it's on my way to work everyday). It has never once not made the sound while driving by it. It maybe be a speed/red light camera or something as well, but I think it has something to do with the train signals. There are several other places it happens in the city (Calgary) as well,those would be okay I guess as I don't drive there as much, but every day has gotten to be quite annoying (ding noise happens in both directions).

What is this from ? A malfunctioning of the physical presence alarm of some kind? Seems odd, as it has nothing to do with being too close to something (it's a 3 lane road and I'm often not surrounded by any, and it has never not gone off).

Thank you for any help! THe Volvo dealer here in Calgary (and the On Call folks) seem to have no idea what causes it.