The sixth-generation Ford Mustang has been caught testing plenty of times, but we have yet to get a clear listen to the turbocharged four-cylinder engine. Well, one lucky Youtube user just so happened upon a camouflaged Mustang on the roads of Flagstaff, Arizona with the a distinct whistle coming from the engine compartment. The video is pretty short, but is definitive proof that Ford engineers are hard at work on a four-cylinder, turbocharged version of the next-gen Mustang.