<<<Find a theme that has only one still image in the background. >>>
Ever since iDVD, probably 1--we found it helpful to create a ten-second 48k/16/stereo silence sound clip in any program that will do that, and one 640 x 480 black JPEG frame in Photoshop or graphics program of your choice.
Dump these two in your theme window and all that obnoxious, pre-formed trash goes away. And it's stable, too. You can set up the theme window to create damage by accident if you only try to turn the existing ones off without putting something back.
I was such a hero when I figured out how to do that.
Remember that rotating globe [shudder]?
Koz