I started this one with one wavy line which I then duplicated and reversed. By rotating it around 8 times, I came up with a nice, but simple design. I then took that and reduced it a little and then superimposed it over the other to get the image you see here. From there, it was just a matter of repeating the image until the page was filled. I then duplicated the whole page and shifted it. After superimposing it over the first page, I wound up with the more complex pattern you see here.
There are many variations that can be done on this theme, and I will keep exploring. I plan to catalogue the backgrounds so that one can choose them for customizing pictures.