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2003 Chevrolet TrailBlazer EXT knocking sound

There is a knocking in the very back of my Trailblazer. It only happens when I first start the car. Goes away within a few sec/min. What is it and how do I fix it

Most likely a rear a/c mode or blend door actuator. Sometimes on this generation of GM trucks disconnecting the battery for a period of time will fix the problem, as the computer will recalibrate the doors operation.

Hello there,
I’ve Trailbalzer 2007, I’ve the same problem above, tried to follow the reset prociedure but it didn’t work, now I need to replace the actuator, it’s the one of the middle of the three on the driver’s side, the problem is I couldn’t reach it from below the steering wheel, do you have a video showing how to reach it?

Look on YouTube