for DSLRs copperhill images the sensor cleaning gurus tell you to take a pic of white sheet of paper at f22 or smaller
http://www.copperhillimages.com/index.php?pr=tutorials
that establishes that the source is in-camera, but in your case not leading to obvious cure, but at least may help if it has to be returned for repair. Then more bad news they give you is that factory cleaned sensors often come back as bad or worse.