Just had a furnace scare - came home from shopping and the furnace was making such a loud clanging sound that I could barely stand to approach it. I don't know jack about furnaces, so I started calling people. I believed it was the inducer motor, based on what the last repairman had written on the service order ("inducer motor making some noise"). At a certain point, it just quit working, and I was getting no heat. I was also getting nowhere with any of the H&AC companies here in town, as no one had this part in stock. The house was getting colder and I was wondering what to do next.
I went downstairs, took another look, and discovered that one of the three brackets that hold the motor away from the unit had broken, which put the motor at an angle (thus all the clanging inside). I looked in my toolbox and found an small piece of metal with a hole in the middle that, amazingly, perfectly matched the bracket screw. Screwing it on like a washer brought the motor back into alignment, and now it runs quieter than it has all year.
Now I'm glad no one had that part, as I would have been charged overtime for the call!