An unrest problem

[Vynd]

I've run into a province where I am having great difficulty keeping unrest under control. With normal taxes unrest goes through the roof in just a few turns, and even with a large army set to patrol and zero taxes it is hard to get it back down again.

There's no readily apparent cause for the unrest, so I've been assuming it is caused by magic sites I can't detect. But is it possible there is some sort of spell causing it? I realize it could also be spies or something like that, but I'm assuming my patrolers would have caught them by now if they were there.

Lastly, I'd be happy to hear any suggestions people might have about keeping the province under control.