That's a strange problem I've not seen before. Very nice image otherwise. Looks a bit like one or two images have lens flare at the bottom left. Have you checked they are all okay ?
-Dithering between light frames will very likely fix this. A stack of closely aligned subs more often produces this effect. The subs will probably look OK.
There's plenty of online info above dithering and the reasons for it. Particularly with dslrs.
With and without shots - Canon dslr.
EDIT: basically, the idea is to avoid overlaying the same or nearby pixels frame to frame. Dithering by 10 - 15 pixels is the general recommendation.
Depending on your set up dithering can be as simple as random movement of the RA and / or DEC axis with the mount HC or automated with one of the dslr utilities. BEOS and similar.
I already dither, but perhaps more aggressive dithering would help - I'll have to check what setting I've got now.
I checked the subs closely and the striations are visible in the individual subs, only in that corner. Maybe the effect was exacerbated by light pollution from that direction on that particular object? I can't see it in subs from other objects which I've yet to process.
