Wierd artifacts

 From:  mickelsen
I am creating some simple 3D parts, starting with 2D outlines and then extruding them. I then cut some pockets in some of them using extrusion and boolean diff. Two of the parts show a funny triangular artifact on them. I've included the drawing so you can see them. They are best seen in the 3D window.
What are they and how can I get rid of them?