Mysterious spots on the ceiling
A few months ago, I noticed light brown spots on the ceiling in my living room and dining room (they share the same wall). At first, I thought it could be leakage from the windows in my master bedroom and office upstairs, which are directly above where the spots appeared. However, the spots are a few inches from where the wall and ceiling meet. The HVAC vents on the second floor, however, are located right above the spots, so I was thinking the source of the spots has something to do with the HVAC pipes. There is no plumbing on that side of the house, so a leaky water pipe seems unlikely. After very heavy rains last week, I noticed new spots in the dining room near the original spot; the shapes are kind of weird, so I don't think the source is a typical leak. I've posted pics of the spots in both rooms (the dining room is the one with the green walls). If I had the slightest idea what was causing the spots, I could call a repairman, but I wouldn't know exactly who to call, since I have what the cause is. Any thoughts?
Here is a link that might be useful: My mysterious ceiling spots