The clunk is usually a manifestation of what are known as "tolerances". Whenever a part is manufactured, it can be tight on a tolerance or loose. Every so often, a transmission will be produced where all the parts are on the loose side, such that you can turn the tail shaft more before it tightens up than would be "normal", despite all the parts in the transmission being within tolerance.
The same can happen with the differential.
When you get a loose transmission paired with a loose differential, you have more clunk than when you have a tight transmission and a tight rear diff.
All cars have clunk to some degree. In many cars it is not noticeable because of sound deadening and further distance from the drivers seating position.
In our Solstices we sit right next to the transmission and drive shaft, and quite close to the differential. For that reason, the clunk is more noticeable.
As a practical matter, there is very little a dealer can do to reduce clunk, short of replacing either the transmission or differential, or both. It is quite possible to have one or the other replaced and end up with more clunk than what you started with.
On the Hanging Limb Highway - 2012
1st 1K - #741