The contact owns a 2017 Ford Mustang. The contact stated while the vehicle was stationary, the headliner became loosened. There were no warning lights illuminated. The manufacturer was informed that the headliner was detaching in the vehicle. The manufacturer informed the contact that the vehicle needed to be taken to a dealer to be diagnosed and the manufacturer opened a case. The vehicle was taken to a dealer where it was determined that the door glass and headliner retainer needed to be replaced. The vehicle was not repaired. The failure mileage was approximately 23,000.