I have actually seen a fair bit of discussion of this where autistic people suggest it's an autistic trait, but I don't think there's any studies correlating the two. It could be one of those things that is just a human trait, that autistic people have latched onto and ascribed to autism. Although, I've only seen it come up in discussions of autism for some reason, maybe just because those are the only communities I'm in where people are constantly examining the idiosyncrasies of their own experience. Then again, your migraine theory holds up - a quick google says 42% of autistic people have migraines, compared to 10% of the general population.

I experience it quite often, and usefully am actually experiencing it right now. I guess it hasn't directly informed my comment, but it's fun to glance up at the white ceiling while typing this and be like "yup, definitely a real thing, can confirm what it looks like". In my case it's very fine-grained, like noise varying on the individual pixel level at quite a high resolution, not like big blobs on a CRT tuned to a dead channel, and is multicolored. But it's also mild enough that it's easy for me to ignore. I think I've seen some people describe it as more obtrusive, blobbier, and/or monochrome, so I guess it varies.

Actually, I went ahead and pulled up an image that's pretty similar to what I experience. It's basically this image but extremely transparent, tiled over my entire field of vision: https://physbam.stanford.edu/cs448x/old/attachments/Noise_Review/white_noise_256_3c.png