I just got my workprint back from alphacine in Seattle. It has a subtle, but noticeable flickering fog, that is very rhythmic and looks as if another layer of graininess or white noise has been added (more so around the edges) to every other frame.
I used 250D film with my h16 bolex in exterior daylight.
Perhaps I loaded it in too bright light? Although this effect is exactly the same on all 4 daylight spools so I doubt it.
I had to ship it to Seattle from Vancouver (the 16mm labs closed down here last month) so now I am wondering if it was the nasty XRAY machine (though I didnt think 250D would be so susceptible to this). Or there is some shutter problem, light leak in my camera, or lastly a problem at the lab.
I will try to upload a file of this as soon as I can accurately video it.