The diagonal lines are broadcast noise/interference, it's independent of the recording speed. I've seen this on an SP recording of an over the air antenna feed.
AviSynth DeFreq plugin (
http://avisynth.nl/users/fizick/defreq/defreq.html) has been very helpful for me with this on multiple occasions. I suppose some other filters like Denoser/Degrainers may also reduce it, but it would also soften/smooth things you may not want to. I don't see that issue when I've used DeFreq.
Set the "show" argument and then try to define fx, fy, dx, dy arguments that put a box around the most noticeable dot(s) seen in the "show" window. May take some time getting used to it, but I find it rather intuitive once I got over that learning curve.
