Without more information its tough to diagnose a problem such as this. Shooting conditions for example. outdoors in daylight? dim light with flash? What shooting mode? Program, aperture or shutter priority or manual mode? How many shutter clicks on the body?
If the camera has a large number of actuations its quite possible the shutter has some issues.
Also if you happen to be close by, i'm in the northeast corner of the state, i'll offer to meet with you somewhere and take a look at it and help determine a cause.
____________________________________________________________________ When no one is looking, Pigs can walk on they're hind legs