I just realized that it may not be the background slide that is blinking. I also have a highlight box over the entire background, which fades it out slightly. I have the highlight boxes setup so they appear to transition smoothly across slides (technically no transition), but I think this is what is blinking. The settings are set to display for the rest of the slide and then the same is used for the next slide.
I've duplicated one of the slides that was blinking and I removed the button but kept everything else the same. This one didn't blink. So it makes me think the buttons are causing this blinking problem.
What is the Button programmed to do?
* Go to next slide
My thought here is that if it's jumping to the next slide, perhaps try using Continue and configure timing so it may appear without the flash?
They were setup to continue.
I figured out a work around by setting the buttons to go to next slide and then adding some space in the next slide before the next caption appears. This works, but it is still a work around.