My car was making an awful noise. I was told by individuals it could be this or that. It sounded like my motor was knocking but would only do it when it was idled low or when it was sitting still. Could it have been the transmission? I did not know. When I was traveling down the highway at high speeds and on cruise, it would not make the noise. It was also worse in the cold weather times. Someone said that the muffler had probably been knocked out of place and since there isn't much room, it was hitting metal and making the sound. Probable since my car sits low. Took it to the muffler shop, they said I needed a new Catalytic Converter. Needed a second opinion. Took it to an individual and he crazily told me that the compressor was bad and was very loose and the Serpentine Belt was "flopping" I thought he was crazy because it is winter and I was not running the A/C. Took it to another individual and he told me the same thing about the compressor and belt. As crazy as it sounds, I got my car back today after agreeing to let them replace the compressor and belt. NO NOISE, my car seems quieter than ever. Hope this helps someone.