I've got one!

Most likely it is the heat shield has come loose, for some reason the right hand bolt likes to fall out and run away. Also have the timeing belt tensioner checked as they have a tendency to stick after 40-60,000 miles and as mentioned above if the belt slips or breaks you can say bye-bye to the top end of the engine. My mother had this happen on her's and I caught mine before the belt slipped too much and caused any damage.