Retrace lines?

[veg-o-matic]

Hi, Gang:
I've been watching my newly-acquired Zenith 5315U roundie (chassis 24MC32) and loving every minute of it. I'm seeing a minor little problem and I'm wondering if it's indicative of something catastrophic.
When the scene fades to black, there are some thin diagonal lines at the top of the screen. Are these retrace lines? At first, they only appeared when the scene went to black, but I'm starting to see them at other times as well. In most color scenes, they aren't there--and I've looked for them!
Is this something I should worry about? Can I adjust them out? Can I just ignore them?
Thanks!