The contact owns a 2015 Mercedes-Benz C300. The contact stated that while driving at an undisclosed speed, there was an abnormal clunking sound coming from the front suspension of the vehicle. No warning lights were illuminated. The vehicle was taken to an independent mechanic, who diagnosed a failure with the steering rack locknuts, observing that the steering rack had become loosened. The vehicle was not repaired. The vehicle was then towed to the dealer, who confirmed the diagnostic result. The vehicle was not repaired. After investigating the failure, the contact related the failure to NHTSA Campaign Number: 18V850000 (Steering), but the VIN was not included. The manufacturer was notified of the failure, a case was opened, and the contact was referred to the NHTSA hotline for assistance. The failure mileage was 70,000.