Im told by a friend that this issue only affects the AAM built axles and not the GM built and designed axles. Like someone already said, it's a clearance issue between the stub shaft and the center pin. It goes away in auto or 4x4 because you lock the front axle and all of thos components spin together at the same speed. They spin independently when unlocked which causes the shaft to rub and the noise. They are working on a fix for these axles. He also said they axle assembly replacement is hit or miss.