Artefacts/noise in printed EPS files

Help. I have no idea what exactly is going on here, and I’m relatively on the ball when it comes to digital imaging. This doesn’t happen all the time, but here’s a description:

After scanning some line art into Photoshop, I save it as an encapulated Postscript file. Now my image looks perfectly normal onscreen. When I print the file out on a Postscript printer, sometimes I get blotches of gray in the white areas of the scanned art. I don’t see any blotches on the screen, but on the hard copy, they’re there. Occassionally, they appear around the corners of objects, looking almost like JPEG artefacts (except that I’ve never JPEG’ed the damn things) but more often they seem to occur in random places in the white of the art.

Does anyone have any idea what is going on here?

Oh, damn. Not paying attention. Wrong forum…could the mods please move it over to GQ?