There’s a federal regulation requiring “quiet vehicles” — meaning hybrid and electric cars — to emit synthetic sounds. That’s because without noisy combustion engines, EVs produce no sound of their own at speeds under about 18 mph, which would make them dangerous to other road users, particularly visually impaired pedestrians. So those sounds are added on. We wanted to know why these cars sound the way they do, so we asked Danielle Venne. She’s the executive creative director at Made Music Studio and helped design the sound made by Nissan’s Leaf.