I also have these brown murky streaks on my walls. I am moving out in a few days, but the six months I have lived here I could smell smoke at random times. These marks are only on my bedroom walls, but they could also be from pests. The previous renter had reported some cockroaches, (which I cringe at every time I think about it) I still don’t know where it comes from but the key thing is it’s only on one wall. That wall, I have noticed won’t let my pin tacks in it. I knocked on the walls and realized it’s metal. It could have something to do with water. So really, the options are smoke, pest droppings, or water. That probably didn’t help much lol :,-) - Luke Hemmings
I think I’d have a priest come and do an exorcism anyway, just to be safe.