Strange marks on ceiling


I recently noticed something unusual about the ceiling in one of rooms in my house (actually, my parents house) and it has me a little concerned. I'm not sure how to describe it though. There are two vents in the ceiling, one is to the south end of the room and the other at the east end. If I lay on the floor and look up at the ceiling, I can see what looks like marks or imprints of some sort of where the metal ducts in the attic go from the entrance of the room (west side) over to the east vent. Basically, these marks go almost all the way across the room.
There are other weird marks that go from south to north but I have no idea what they are. There are about 3-5 of them and they're a sort of light brownish color that are about 4-6 inches wide. My first impression upon seeing them is that something in the attic got too hot and it burnt the ceiling. The other thing I thought it could be was some sort of water damage but I'm not sure that's it.
When I go up to the attic to look, I don't see anything unusual but I'm not an expert and I'm not sure what to look for. There's nothing in the attic except for the attic fan, cable tv wires, antenna wires, metal air ducts, electrical wiring, and insulation. It's not used for storage as it wasn't designed for that.
The only thing I know is that once, two months ago, there was a small amount of water dripping from the corner of the east vent in that room. My father checked it out and it hasn't leaked since then but I don't know what the problem was. Sometimes, when it rains, it does sound like there's water dripping in the attic but I can't confirm that.
Any ideas on what could be going on with the marks from the air duct and the brown marks?
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Probably not enough insulation on the ducts and you get condensation in summer when its real hot and the AC is on.
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Mike S. wrote:

I think ransley is correct or nearly correct. The water coming from the duct vent suggests poorly sealed joints in the duct work. The series of marks probably match joints in the duct or in the insulation. I think the joints have to be sealed and then the insulation made continuous. A barrier should be on the outside. TB
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Mike S. wrote:

I agree with the others. Sounds like moisture. A/C is one likely source. You may need to go up there and take a look to verify the problem and to correct it.
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Mike S. wrote: ...

I agree mostl likely the water stains are the color -- the pattern(s) might be the drywall joints. Quite often w/ a small amount of water, the paper surface sheds the water and but the joint compound/cracks between the sheets absorbs it and "telegraphs" through to the other surface...
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Mike S. wrote:

or on the duct. Where I differ slightly is that I would suggest the condensation might be the result of poor drainage from the drip pan beneath the A/C coil. That can lead to excessive humidity and even free water in the ducts. Check that the drain(s) is/are clear.
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wrote:

Got photos?
later,
tom @ www.Consolidated-Loans.info
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