Strange looking black artifacts

I started a new scene today and there are black artifacts on some objects (First Picture)
So I applied the subsurfe modifier, removed doubles and recalculated faces. Most of the artifacts dissapeared but there are still some left (second picture) which I can’t get away.
I hope you can help me with this problem.


Since it looks like just simple extrusions, try deleting the top of the column, and redoing it. You definitely have some overlapping faces or inverted normals.