This bulletin applies to 2010-2011 Cadillac DTS models equipped with the 4T80E automatic transmission and built after Feb. 1, 2010. A final gear whine noise at speeds between 15-30 mph may be heard. This condition may be caused by the transaxle final gear drive.
Road test the vehicle and evaluate the noise at about 19 mph with the radio off and the HVAC fan set on speed 3. Compare the condition to a like vehicle (that’s assuming you have another 2010-2011 DTS handy).
If the complaint vehicle is not louder than the like vehicle and the noise can’t be heard with the radio off and the HVAC fan set at speed 3, GM notes that this is considered a normal characteristic of this vehicle.
Big help, huh?