This. Almost every time I've had any corruption problems, it was preceded by the little under-voltage rainbow icon appearing. Also, if you have things plugged into USB, consider setting the usb_max_current setting to 1 in /boot/config.txt
As far as I know there's a task running on the "GPU" (where quite a few things are assisting the ARM CPU showing the screen, playing audio, actually bootstrapping the ARM, ...) that provides this icon as a feedback to the user.