Heres what i mean by the noise, you can see it clearly here:
Close up:
It almost looks like blocking when i look at it close up like this, maybe it is not noise, but a type of compression artifact inherent in LD video? I thought it was noise at first...
When i mentioned about the msu noise generator i figured you should probably stretch it so it matches (just the noise), but what if instead of using a filter you take a sample of black from one of your captures with that noise (whatever it is) and overlay it on the dvd footage with avisynth? Maybe add a bit of blur to the dvd footage first before the overlay might help blend it in even more.