Thanks everyone. I'm not worried about the dust!
I actually read that banding post before posting this. I've tried a couple of memory cards.....Now that I think about it, the only cards I've used are HCSD cards. The camera itself is an *ist DS, which according to dpreview and the manual mention nothing about HCSD cards....I wonder if this could be the case. I'll have to check that out....I can't really see why that would make a difference though.
I hope I don't have to send it to Pentax. It's modded for IR photography.