I made myself a procedural brushed metal texture. I use it to render CAD designed parts in blender. On most of the parts the texture looks great. But sometimes there are strange artefacts in the lightnig, as if the faces are not planar. I've tried to retopoligize the mesh a bit, but somewhere, there are always this artefacts. The strange thing is, I symmetrized the mesh, and the mirrored faces look just fine.
Has someone a clue, what this could be?