New part issued by GM. Old par defectiveIt's the tension washer between the axle and hub. The nuts are usually changed at the same time, but the washer is the main cause. Full thread with details linked below.
Click or Pop noise from front on Accel or Decel
My dealer tried torqueing and then changing the axle nut before they finally gave up and changed the whole axle. Covered under 5/100 warranty. Just changing the washer would have fixed it. But, since GM was paying, I didn't car about the overkill.
Part number 11611687.
Old thread, yes.. my car still runs. I’ll drive till wheels fall off