Some slicers will cause each layer to start printing at the same point on the perimeter each layer. Skeinforge, the slicer for replicatorG, always starts my prints on the left-front corner of the print. This can appear as a 'seam'. That might be what you're seeing. Some other slicers allow you to set a random start point on each layer, which would minimize the appearance of that seam. I pretty much only use repG, so perhaps others here can offer suggesttion on slicers.

Cheers,

John