PDFXview.exe is PDF-XChange Viewer and at that moment in time it was OCR processing a 664 page image PDF. So, yes, I use it quite frequently but, no, I'm not typically having it run an OCR scan on a huge document. I far prefer it to Adobe Reader. Believe it or not, I know that wasn't the problem. Most of what gets eaten up during that sort of processing is CPU cycles as opposed to I/O.
I have two different Gmail accounts open at once, and you can't do that in a single browser session (even with multiple windows). I can, however, use either Firefox or Chrome exclusively for some set period of days if you want to see if that makes a difference.
If this were directly "end user program" driven I'd expect that the activity would cease once I exited "the offending program." I have yet to find something I can exit that makes the activity cease, which is why this is so *&^%(# frustrating!! [And, of course, that *&^%(# is not aimed at you.]