white box flash when new page loads

https://bkqualityconstruction.com/

This site worked great. Then I have been adding things! Oh boy… newbie. So now when I click on menu pages there is a white box that flashes as it loads. This does not happen on the about page but does happen on all the rest. Also there is a white strip at the bottom of the home page that was never there before. This showed up after I worked on putting columns on the about page…. don’t know if that had anything to do with any thing. Hope I explained it well enough someone can under stand. thank you for any help