Not to further digress, but to refine what has gone before, here is a much better FM stereo noise distribution chart than that which I attached to post #21. It is from the FMX patent document.
One could also draw up a similar chart for the FM subcarrier case. This would be a case of triangles upon triangles plus pre/de-emphasis effects, whereas for the AM subcarrier case it is triangles upon rectangles, plus the pre/de-emphasis effects.
Cheers,