Thanks to the answers and suggestions to my plea, I may have figured out what's happening with SyncTeX scribbling on my monitor.
It was suggested that 'texlive-extra-utils' is where synctex comes from, but that's not installed here. So more than one package must bring it in as a dependency or something. Here, I'm pretty sure, it's Evince. I have a Python script running that tells me every hour to get up from the keyboard and get a little exercise. That script runs Evince to display pdfs of the notices. When I kill the script, the garbage no longer appears. And other Python scripts don't do that stuff. The problem now is that those notices are good for me. I've looked for other pdf viewers, but there's nothing in the repositories anywhere as nice as Evince for taking up the entire screen and enlarging a pdf. Anybody know of a civilized, bug-free pdf viewer? (will display full screen with no or thin borders, allows for manipulating size and position) -- Glenn English