and an uneducated one at that: I've heard some report that the belt tensioner shock absorber can sometimes make a slight rattling noise when it gets worn out. On the m103engine, this little black shock absorber is located on the front of the engine, between the left-front corner of the head and the coolant thermostat housing, extending down at a slight angle out of sight under the belt idler pulley. I think your car has the m104 engine, but I believe it's in a similar location. You can try using something as a stethoscope (like a long screw driver) and listening to it while a helper starts the car first thing in the morning. You've got nothing to loose by checking it out (except watch your fingers and the fan).