When shooting with the D70

there may be some dust particles on your low pass filter .To check this have a fully charged battery in your camera .switch on the mirror lock up to on from the menu exit menu and press the shutter now remove the lens and inspect and blow any dust on the low pass filter with a blower brush donot attempt to clean yourself with cotton or any cloth as it may damage that low pass filter reattatch the lens and shoot .Hope this might solve your problem if not have your camera's ccd checked for any dust on it by a professional.
Kamal GO
brijwasistudio@gmail.com