I started hearing a groaning noise coming from the passenger side dash. It sounded like something was rotating and during a portion of the rotation it was rubbing or catching something. This continued all the time with or without the heat/ac on. The noise eventually got worse, then stopped. Once it stopped, I noticed that only blazing hot air came from the passenger side vents. I could feel the air go from very hot to a mix with cooler air and back to very hot every 2 seconds. Some online research says it is the blend door actuator and it requires tearing out the entire dash to access it. I bought the actuator, but haven't installed it yet.