mysterious grainy texture

I have a simple object I made by extruding part of a UV Sphere and when I apply a texture with Ray Mirror enabled one of the faces has a strange grainy texture on it. If you do F12 on the following file you will see it clearly (the render will only take a few seconds).

Any ideas what is causing this?


In Edit mode select all (A) and W >> Remove Doubles.


Thanks alot Fligh! I never could have figured this one out myself (: