I've seen a lot of questions (including one on this site) about condensation on bathroom vents. However, they all seem to take place in winter, with consensus being that as the warm air from the bathroom travels slowly to the outdoors, it is cooled off and condenses in the pipe and drips back down to the fan.
However, I am having this problem in the peak of summer, where it's intensely hot and humid outside, and nice and cool inside. This happens in the downstairs bathroom. I believe that it is vented outside, to the side of the house, not the roof. If I am correct, then the exhaust pipe has to traverse the length of the living room to get there, maybe 10 feet or so. This is only a half bath, so there isn't even a shower creating humidity.
Any ideas would be appreciated! The dripping is driving me nuts.