nice sketches! I like a lot of the ones you posted.
Before I give any criticism though, I'd like to know if you use references when you draw these? Or are these out of your imagination/observation?
Also, I agree with what Krith said. The pieces would be even more polished if you apply different amounts of pressure to vary the widths of your lines (or add some shading).
I think the grainy quality of the scans has something to do with your scanner settings, possibly the resolution. If you resize it and adjust the contrast options, the image may appear closer to the original.
But as you mentioned in my thread about technology... it drives me nuts sometimes too. orz
treat me like a free disease