It sounds like you have dust on the sensor. Two options. Either send it in for service or learn how to clean it yourself. There are a few web pages out there with step by step illustrated instructions. Do a Google search.

Specks on the sensor filter certainly could be the problem, but you should make sure of it. The best way that I found for my D70 is to take a picture of say a lightbox or other uniformly lit area, overexpose by 2 or 3, use the smallest aperture to get a clear contour of the dirt specks and manually focus on infinite. If you have specks, they will very clearly show as dark areas. Be careful how you go about cleaning. I have used the method described on www.cleaningdigitalcameras.com with great success. Stay away from Hurricane blowers and SpeckGRABBERS! Good luck.

Frans Waterlander
frans2001@netzero.net