Sudden streak on Dimage IV scanner image?

I was scanning slides the other night with my Konica-Minolta Dimage scanner and everything was fine. Today it is putting a streak across the entire upper area of the image. The streak is dark with slides and light with negatives, and I know the streak isn't on them. I've never had a Dimage apart in all the years I've had it, so I'm not familiar with it's internals. Is this something as simple as a piece or dirt or dust (hope so)? Or something more serious? Thanks.