Not to go off topic but the Toyota Prius sounds the same way at times, my parents rented one a while back and it was making that sound. Part of the reason why that car is a personal favorite of mine, when I heard it do that the first thing that came to mind was the hybrid buses here in NYC, not to mention this cool screen it has in the dashboard showing how the hybrid system is working in the vehicle, yeah, I was foaming. :cool: