Q: Vibrating Macbook Air

I have a new Macbook Air and I'm studying overseas in France for 6 months. I plug my computer into a transformer and then into an adapter so that it will fit in the power sockets here. It has been vibrating oddly when I charge it - whether I charge it on high or low watt settings on my transformer - and it's starting to make me nervous. Has anyone else experienced this? Is it the foreign power source? Is it safe?