What is the cost of an air conditioning gear? on 2008 Chevrolet Impala

There is a knocking sound coming from the area behind the glove compartment when the motor is shut off.
We were told it probably was a gear.

Asked by for the 2008 Chevrolet Impala
Can't tell without checking it myself,sorry.
1 more answer
I don't know the Cost of an A/C Gear, I've Never heard of an A/C Gear, But I have had this Noise coming from the car Even when the car wasn't running and the Key not even in Ignition! It was the "Blend Door". This is the door that opens & Closes when you change the Vents, Say like from the Upper Cabin Compartment to the Floor.
I don't know the cost to Repair or Replace, Mine Quit on it's Own Thank Goodness!
I could be sitting out on my Porch & it would just Start Up On It's Own! I wouldn't think that it would be an Expensive repair, Hopefully a Relay or something Like that. Maybe it will Quit On It's Own, Good Luck :-)