My Saab stopped on the highway as I was driving the speed reduce and then it stopped. Before that I was hearing some rattling noise for several weeks. Took car for oil change machanic said possible pistion loose. After it stopped I was also told not by a mechanic that it could be the starter alternator. I would like to keep the car if its not any major engine problems. Also in addtion to the rattling noise the car sounds very loud overall. No exhaust issues. What do you think the problem is.