I apologize ahead of time if there is an existing thread addressing this problem I haven't been able to find it. I would appreciate it if someone could direct me if a thread exists.

I have a 2011 Q7 S line Prestige. There is a problem with my 4 zone heat. In cold weather, after the car is warmed up, when I turn the heat on, hot air flows from the front vents but the rear vents blow very cold air. Can anyone help me diagnose this problem?

The thermostat was replaced recently and a few times in the recent past, when the hvac system was on, there was an intermittent squeaking coming from the left side (driver) of the cabin. The sound was rather loud but I was never able to pinpoint exactly where it originated. It seemed like it came from the rear of the cabin. It also seems that the B pillar vents pointing to the rear of the cabin have less air flow. This airflow is also much cooler than the front air vents.