Having this issue as well, played through it before without issue. The only thing that's changed since I last played it a year ago is my OS with went from XP to 7. It also started during and after soul cairn. Tried everything I could find on the web such as installing VC++ 2012, DEP exceptions, etc. And still get it. It's random and I played fine for hours with Dawnguard installed. It seemed to start during the Beyond Death quest and has been happening since. Don't know what to do. Don't know why it'd work fine on XP but not Windows 7. EDIT: Curious if this is simply related to the quests and finishing them will make it go away. EDIT2: It did not. Got one after finish the entire quest line and going after the standing stone crown. Though at this point I'm positive it has to do with something that gets flagged after entering the Soul Cairn. Possibly those stones that drain your health. But I haven't heard the sound from them or seen glimpses of their effect anywhere like I've read in the odd post around the net.