I had a 60 Ford pickup with a six that made a disturbing whistle that came on when the engine heated up. I never could figure out what caused it. My remedy was to park it near a use car lot that had a sweet looking 55 Chevy I wanted to buy. After the engine cooled off I whipped it into the car lot and proceeded to buy the Chevy. The salesman drove it around the block (not far enough to heat it up and cause the whistle) and we made the deal. A week later the car lot called to ask what the devil was that infernal whistle. I told them I never could find the cause and that was why I sold it to them. That is the one and only time I ever got the best of a use car salesman.