The optional mode works like any active exhaust system. When you select Quiet Mode or Quiet Start, a set of baffles in the exhaust system close, dropping the sound to about 72 decibels. Ford says that's about 10 decibels less than the standard Mustang GT. A lot of cars offer similar systems, though the Mustang has a bit of a party trick: scheduled quiet hours. For example, an owner can set the exhaust to automatically switch to quiet mode from 9 p.m. to 8 a.m.
Switching to and scheduling Quiet Mode is just like changing to any of the other exhaust modes. Cars with the 4-inch screen can find the mode in the settings menu. Those that opt for the upgraded 12-inch digital instrument cluster find the setting in the pony menu. Once you're out on the open road, you can simply switch it back to Sport mode like any blue-blooded American.