Genius? Dunno about that. It's just something in Carrara I actually remember messing with before. When the process is easy to knock out like that, it's hard to not just give it away.

I know some plugins make artifacts akin to what you describe. But that usually involves cases where you get a reflection of a reflection. (ie: Sparrowhawke's otherwise nifty experimental falloff shader does this.) I still keep these plugins, but move them into a folder outside of the Carrara directories for times when they cause problems. Also in certain lighting conditions (like non-moving direct light in an outdoor scene), it might be good to set the lighting for static scenes under render settings or the background gets noise that looks like video snow.

As to other things, who knows? Could be compression or something like that too. I usually just render to frames for animation and use VirtualDub & Xvid, since they're free and present few problems. (PC only though. I dunno what is comparable to vdub on the Mac side, sorry.)

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Barbequed Pixels?

Your friendly neighborhood Wings3D nut.
Also feel free to browse my freebies at ShareCG.
There might be something worth downloading.