Rattle at engine startup

What is your question?

2003 Lincoln Aviator with 117,000 miles. When starting engine, a rattle lasting only about 3 to 5 seconds comes from front end. Took to dealer, who kept for 1.5 days but since sound would only last for a few seconds wouldn't/couldn't diagnose or condemn any part. Suggested it might be timing chain, but nothing conclusive. I have a Ford ESP warranty on this vehicle through 131,000 miles. If this would become a potential major repair at some point, would clearly want the ESP to cover. Any thoughts on possible causes and/or dealerships utilization of ESP coverage are appreciated. Thanks