"Knocking" noise under dash 03 Sierrra

[barry34]

I have a 03 Sierra SLT Z71. Bought it new off the lot. After about the first year and barely out of warranty, I have experienced multiple failures with electrical components. Now, I'm getting a loud knocking noise at startup, that appears to be coming from the drivers side under the dash and the air now only comes thru my defrost vents. At startup, I get around 7-8 loud knocks. No matter where I change the control setting, the air comes from the defrost vent. truck has been mechanically sound but an electrical nightmare.

[txab]

Actuator motor. I'd bet