I have some stubborn spots on the sensor of my D700 that don't come off with the automatic sensor cleaning or by blowing air onto the sensor with the camera facing down, and some of the spots are quite annoying, because they can easily be seen in the pictures even at f/5.6. I have never touched the sensor with anything. One small area is particularly worrying, since the spots are in a strange pattern. I'll attach a 100% crop of it so you can see. What do you think is it, and how do I go about removing this? I have read Thom Hogan's guide on sensor cleaning, and I am willing to try it myself, but I don't want to do any damage. This doesn't look like ordinary dust to me.