This is probably the result of a humidity problem inside your house. High humidity is forcing condensation to form against those particular vents. I suspect they're the ones closest to your air handler. Either they're colder than the other nine vents, or they're located in a more humid area of the house - perhaps closer to a bathroom. Take steps to reduce humidity and the problem might relent. This begins by improving gutter drainage and grading around the perimeter of your home to keep moisture out. You might also consider a whole home dehumidifier. Whole home dehumidifiers are permanently installed inside of HVAC systems, and take far more moisture out of the air than the HVAC system could ever do itself.