Ondra said several times that light noise bug is still fixed, but i still do not believe him... :) I would try to remove all corona lights from the scene and use only emissive materials ;)
I think that as long as CoronaLight is internally handled differently than emissive material, there will always be this problem, and it will be just patches on top of patches, so they issue will be deeper and deeper and harder to reproduce.
This makes me really sad as it makes Corona very unreliable in more complex scenes and makes the problem very hard to track.