Gray overlay

I work for the Wisconsin State Journal. We subscribe to a service that archives past issues. We've found recently that many of these PDFs have a gray overlay, aren't as sharp as they used to be, and are giant files (21 MB versus 3 or 4 typically). I assume it has something to do with how they're scanned in, but is there a way, after the fact, that we can remove what appears to be a screen over the pages? When I rapidly re-size the files (Control+wheel), the gray disappears for half a second and I see clean black-and-white text, so it must be some sort of layer. We've tried working with the folks who scan the documents to see if the problem is being caused on their end, but in the meantime can we do something as the end users?

Here are two snips: The first shows how the pages used to look, and should look; the second shows the gray overlay.