Just making this bulletin that GM send out while back on the clunk a separate thread so it's easy to find.
Quote:
Information on Driveline Clunk Noise When Shifting Gears At Low Speeds
Models: 2006 Pontiac Solstice
with AISIN AR5 Manual Transmission (RPO MA5)
A Pontiac Solstice equipped with a manual transmission may exhibit a clunk noise when shifting gears at low speeds. The noise may be present during low speed driving maneuvers, such as driving in stop-and-go traffic or in parking lots, which require declutching and shifting.
Some amount of driveline clunk is normal due to the design characteristics of the driveline system. While some owners may find the clunk noise objectionable, it will not adversely affect durability or performance.
Whenever there are two or more gears interacting with one another, there must be a certain amount of clearance between those gears in order for the gears to operate properly. This clearance can translate into a clunk noise whenever the gears are loaded and unloaded quickly. Comments of driveline clunk are usually not the result of one individual component, but the result of clearance present in all of the driveline components.
Because all components in the driveline have a certain amount of clearance by design, changing driveline components may not result in a satisfactory noise reduction.