Luxury vehicles make a statement—but too often, you can’t hear it over the roar of their engines. So the makers of top-line craft are dummying up the decibels, with a technological silence that’s 24-karat golden. Indeed, keeping quiet has become a science of its own. Whether at sea, in the air, or on land, merely piling on the insulation or amping the scrambler frequencies isn't enough. The most effective solutions for shielding pampered passengers now require nothing less than restructuring the entire architecture and engines of boats, jets, and car engines.