I could be wrong, but those look like classic dust spots to me. Unlike my D5000, for some reason my D7000's sensor is a dust magnet. I personally subscribe to the lens/ pump theory, since I use mostly zoom lenses and the dust seems to accumulate regardless of how careful I am when changing lenses (which is VERY careful). (I mostly do nature and landscape photography, so I am out in dusty places a lot.) In any event, regardless of the cause of the dust, I have learned to clean my own sensor. I use the Photographic Solutions Sensor Swabs Type 2 with Eclipse solution. First, I blow off as much dust as I can using a Rocket Blaster. Then, I swab, following the instructions. It generally takes 1- 2 swabs to get the sensor spotlessly clean, but I have had occasions where the dust was more stubborn (or they may have been oil spots) and it took 3 or 4 swabs to get the sensor truly clean. I also invested in a Lenspen SensorKlear Loupe, which is a great help in cleaning the sensor. The loupe has internal lights that shine down on the sensor and, with the magnification, you can easily and clearly see the dust (the included button cell batteries are awful, however; I eventually bought one of the cheaper substitute types which last 10 times as long and cost about a third as much).

If you own a D7000 and have taken a substantial number of shots with it, especially if you change lenses or use less expensive (i.e., not well sealed) zoom lenses, I can almost guarantee you that you have dust on your sensor, even if you haven't noticed it yet.

Good luck with yours.

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