iMac screen issue - flashing magenta and green squares that are 'erasable'
I've had this issue for quite a while. As you can see in the video, my iMac screen occasionally gets these flashing magenta and green squares. Most of the time, they can be 'erased' as shown in the video. When I reposition the Chrome browser window, it makes the squares disappear. Sometimes the squares reappear right away, sometimes they move to other parts of the screen.
Other potentially helpful info:
This can start at any time, sometimes after iMac has been on for several hours and sometimes when iMac is initially turned on.
I have a second Apple 27" monitor attached, the squares appear on that screen as well.
iMac, 27" mid-2010, 2.8GHz i5, 16GB DDR3, ATI Radeon HD 5750 1024MB
macOS 10.13.6
Any ideas? It gets really annoying, and I'm hoping it's not the sign of something bad about to happen to my iMac.
iMac 27", 10.13
