National Public Radio: You probably recognize the sound of a Harley motorcycle. If you don’t, try roaring “potato-potato-potato” into a microphone, and you’ll be close. But today there’s a much quieter motorcycle sneaking up behind the Harley, the 2010 Zero S street motorcycle. And if you don’t love the sound, your neighbors sure will. It’s a completely silent, pollution-free motorcycle created by the California-based company Zero Motorcycles. The founder, Neal Saiki, designed world-class mountain bikes for …