My experience with burning anti-freeze is that it smells sweet, kinda like syrup. This doesn't smell like that. But maybe it smells differently coming out of the exhaust.
No massive weather change, and it's been happening consistently for about 2 weeks now.
Didn't touch any of the head bolts (had the same thought), but removing the valve cover seems like it could be a culprit somehow.
Thanks for the ideas so far, I'd really like to figure this out.