This bulletin applies to 2016-2018 Cadillac XTS vehicles. Some customers may comment that a vibration is felt under heavy acceleration around 20 mph which can be felt in the seat. This condition may be caused by a second order vibration from the cardan joint. The suggested fix involves installing a 4.5mm-thick shim on the top of each RDM isolator bushings.
Perform the service one side at a time, always leaving one of the bolts engaged.
With the vehicle raised on a lift, remove one of the differential bolts that pass through the RDM bushings. Loosen the opposite side bushing bolt. Positon the 4.5mm-thick flat washer over the differential mount washer. Loosely install the bolt enough to support the differential. Remove the opposite bushing bolt and install a 4.5mm-thick washer over the existing differential washer. Install the bolt, then tighten both bolts to specification. The shims are available as P/N 11562546.