funky square artifacting in the blender smoke simulation

Hey!!
I’m running into some crazy issues with the blender smoke sim. Has anybody else encountered strange square edges like this, or found a way to fix 'em? It would be much appreciated!!
These are showing up in just about every fire sim I’m doing… maybe it’s my shader?
I’ll be releasing a tut on realistic fireballs ‘n’ junk like that this summer =)