Can you still hear the fan going? It's most likely the infamous vent mode door actuator. It's what controls if you want the air at your feet face defroster etc. It fails on all kinds of vehicles. There's a diy on how to do it under the section. You posted this on.I got a 2011 titan pro 4x and today when I turned A/c on it started making a loud popping noise then stopped working. The sound was from under dash on passenger side. What can I check first?