Dotted lines - bad burn or bad DC?

[vsp]

Silly question of the day:

My Dreamcast occasionally displays faint vertical lines when displaying certain graphic modes. Up until now, the most obvious offender has been Soul Calibur -- not all, but some of the stages produce these dotted lines in the background. They're dim enough that they're not a big problem, but they've been there since date-of-purchase (which was date-of-US-release). Most games (including some FMV-heavy ones) display with no problems or lines at all.

I recently obtained an image of Evil Dead; it burned successfully, but it was by far the worst offender I've ever seen in this respect. It displays several lines of big green dots (not the small, semitransparent dots some other games displayed), which stand out during gameplay and are quite an eyesore.

What are the odds that it's a problem with my Dreamcast's GD-ROM drive, or that I simply have a semi-corrupted image, or both?