The contact owns a 2021 Toyota Sienna Hybrid. The contact stated that while driving at an undisclosed speed, there was an abnormal rattling sound coming from the second-row seats. The message to ‘Check Rear Seats’ was displayed. No warning lights were illuminated. The vehicle was not taken to the dealer or an independent mechanic. The vehicle was not repaired. After investigating the failure, the contact related the failure to NHTSA Campaign Number: 25V086000 (Seats); the VIN was included, and the vehicle was repaired. However, the contact was informed that the remedy was for the third-row seat only. The manufacturer was notified of the failure, a case was opened, and the contact was referred to the NHTSA Hotline to report the failure. The failure mileage was 169,000.