A lot of cars have warning chimes, buzzers and bells to warn you of all sorts of things you have never even imagined going wrong. The Japanese manufacturers seem especially keen on them.
It could be an actual fault with a door-ajar or seat-belt warning chime or it could be a new habit the sat-nav has picked up. Have you checked the oil level and the level of coolant in the overflow-tank? Plenty of cars will warn you when these items need attention, and, since they’re not everyday events, this could be the first time you’ve experienced them.