[Walt White Coupe]

^^^
Sounds very similar and why I eventually just gave up as have others on this tread.

Hope you keep with it. But because the rattle goes away once the engine heats up, it's almost impossible to troubleshoot where it's coming from even if they do hear it with the engine cold.

When I had the SA in the car, I played the recording of the rattle through the car's audio system. Then I drove the car with him and once you know what you are looking for, you can hear the rattle even when it's very faint but he couldn't hear it. Like you said, frustrating.