I just randomly ran into this post and can relate. A while ago, I noticed weird horizontal lines running up both the Viewer and Canvas windows when previewing footage (almost like an old VHS tape). This sounds like the same issues you're running into.

I got really frustrated trying to find a pattern to the distortion and finally solved the problem by moving the Audio Meters. For some wacky reason, anytime the Audio Meters window is touching (snapped beside) either of the Viewer or Canvas windows, the lines show up. After rearranging everything so the windows are no longer snapped into place next to each other, the issues went away. I haven't seen the lines in months.

I'm a little late to the thread here, but hopefully this info helps out some.