My suspicion is that the noise is more visible in the blue areas of the shot, as the blue channel typically has more noise.
Try applying noise reduction to the blue channel only (or predominantly) in Photoshop. Alternatively, some noise-reduction programs can work on specific colors as well.
Ah! Great idea. I'll try this w/Dfine, and don't know B&W enough to know which colors effect what aspects of a shot, but I can also play around w/the blue in SEP, as well.
And you're quite correct. This shot in color is not just blue, it's BLUE, so that's where I'll start work.
Thanks for the tip about color and the suggestion!