Light map adding dark streaks to textures

This one is blowing my mind as it seems completely random. I'm working on the "Survival Shooter" tutorial from Unity's website, and when the light map finished baking (I have "Continuous Baking" turned on) suddenly these streaks started appearing all over random textures, like someone had lightly dipped a paint roller in grey paint and went nuts on random surfaces.

Normally I'd think it was some incompatibility between 4.6 and 5, but I've had this same problem happen on a model I created from scratch within Unity 5. I'm not quite sure how to fix this; I'm sure it's as simple as adjusting a setting, but I don't even know what to call this bug so I don't quite know where to start looking.

Looks like bad lightmap UVs. The spiral element turns up quite a few times, could be the robot head and arm.