Most helicopters are built for hovering, not for speed. But the Eurocopter X3 is built for both. The demonstrator tilt-rotor aircraft proved as much when it set a pair of air speed records earlier this month.
Helicopters make a lot of noise because of a physical phenomenon called blade-vortex interaction. Eurocopter engineers have developed a new kind of rotor blade that attenuates this problem. It's called Blue Edge, and—as you can hear—it works beautifully: