The entire world is covered in UFO sightings. Don't believe me? Check out UFO Stalker where they list the most recent ones and update them live. Of course a few are going to find their way drifting over Michigan skies. Like this one:
While this one might not be part of the Detroit Underground in a literal sense, maybe it's a part of the Detroit Aboveground.
Waiting for the Phoenix to rise
2 days ago