I've noticed some small waiter staining around the ceiling air vents. I thought this might be due to condensation (it's regularly 80F outside and I keep the temp around 73). I went into the attic and it does appear that the air ducts are insulated? The house isn't a year old so I'm hoping this isn't a bigger problem.
I've requested an HVAC expert and my home warranty to come look but in the interim I'm curious if others know of any common causes behind this issue.