I'm not entirely sure, but it may be something called artifacts. I don't know much about them, but I think they have to do with the layout of the geometry. It only occurs where geometry curves too much at one point or there is a lot of geometry or something like that in one, small place. Who knows, maybe it's not this at all. Perhaps someone else can elaborate. In the mean time, why don't you batch render a short animation of some simple poly and nurbs objects and see if it re-occurs there. Also, it just might be your production quality in the render globals. I have never batch rendered at the lowest quality, but that's what you may be doing since that is the default. Just change the preset to Production Quality if you haven't already.