What are you using to degauss? A handheld degaussing coil, or something less powerful (like a drill)?
If you've degaussed it with a coil, and you still can't get it out, you might need to readjust the purity. Display a solid red screen, and you should not have any blotches of other colors in it. If you do, and they won't degauss away, adjust the purity with the pair of adjustment rings closest to the yoke.
Your "wave" is probably the filter cap (C606, IRC) going bad.
-Ian