Hi actually, I'm still running PPC although Intel is in the not to distant future. Of the folks I know rendering Carrara daily on Macintel, this hasn't cropped up before. 

**This is not an answer but I looked more closely at your screen capture: The anomaly looks like two missing polygons - it's also occuring on the same location on the objects. I'd open the shape up in the Vertex Room and double check that 1) the Normals are pointing outward, and 2) that there is actually a filled poly there. I've had something like this happen several times on geometry exported from other programs. (on very similar subject matter by the way!)