The contact owns a 2020 Ford F-150. The contact stated that upon starting the vehicle, there was an abnormal rattling sound coming from the engine compartment. After the vehicle reached normal operating temperature, the rattling ceased, but the failure became a regular occurrence. 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 Customer Satisfaction Program: 21N03. 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 unknown.