I've listed this issue in the bug list thread. Turns out it's not just god rays.
I've disabled everything and played with the INI. It only goes away if you disable the volumetric lighting pass in the INI. Just disabling godrays doesn't fix it for me. Problem is, disabling volumetric lighting affects everything and it looks over bright and very static.
Sadly, it looks like a bug. It also way over blurs any transparency to 1/4 normal resolution. As it only happens in certain areas looking in certain directions toward lighting [or into shadow from the lighting] maybe it'll be specific enough to run down easily.