Hello,
That knocking noise is probably a blend door actuator that has gone out and needs to be replaced. Here is a guide that will help you see what I am taking about with a diagram (below) that will show you what it like on your car.
https://www.2carpros.com/articles/replace-blend-door-motor
Please let us know what happens, we are interested to see what it is.
Cheers, Ken
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Sunday, July 9th, 2017 AT 1:28 PM