About a week ago when closing the passenger rear door of our MKC I heard a rattling noise come from under the car. I then knelt down looking under the car then closed the door again. The noise was coming from the metal shield on the bottom of the fuel tank. I assumed that maybe a pebble or small rock was on top of the shield causing the noise. On Wednesday, my wife called me and told me that she thought that she was dragging something under the car. She looked under the car and didn't see anything. I told her that I had heard a noise about a week ago and thought that maybe this was the same issue. Last night I investigated the metal shield under the fuel tank and noticed that one of the small nuts was missing from a stud that that protrudes through the shield. This stud is probably attached to the fuel tank strap. I found a fastener in my can of nuts and bolts to temporarily keep the shield in place and from rattling. My local ford dealer is going to order the proper fastener which is a 10mm nut. Not a big deal, but this type of small annoyance is frustrating. The only other problem we have had with the car is at around 4000 miles the alternator had to be replaced which I posted on the site earlier. Otherwise, the wife is happy with it and we have about 10,000 miles on it.