Afterburn -- Intersection Artifacts?!

Are you using Lambertian/Phong shading? I suspect you're seeing those 
intersections because they're where one sphere's normals meet the normals of the

next sphere.

Try not using any of those shading methods. If you really like the way they 
look, try using Normals:Noise with zero shape influence ("S Inf.").


Those shading types are there as an alternative to raymarched self-shadowing. 
Real smoke doesn't have normals, but it can still look like it has a 
surface simply by the effects of its own self-shadowing. Self-shadowing is 
computationally expensive, though, and sometimes users don't want strictly 
realistic smoke & clouds, so those normal-based shading methods are there.
Try 
using self-shadowing (by itself) instead. You mightn't want such a tiny 
step-size if you go that route, though.