Thin red vertical line on desktop
I've seen other posts about a thin red line on an iMac screen. Mine is a little different in that it's only on the desktop, but doesn't show up on any opened documents, web pages, etc. It does show through any icons that happen to be on that part of the desktop. I don't think it's an LED issue--I'm assuming that would affect the screen view of documents as well. Any theories? Thanks for your help.
iMac 27″ 5K, macOS 10.14