No one can tell you what it is.This is the operating characteristic of your transmission and customer do object to the noise or clunk and dealer discourage the repair. This is TSB 03-07-29-004G. Let me give you a partial copy.
December 15, 2010
Manual Transmission Operating Characteristics
Manual transmission operation will be affected by temperature because the transmission fluid will be thicker when cold. The thicker fluid will increase the amount of force needed to shift the transmission when cold. The likelihood of gear
clash will also increase due to the greater time needed for the synchronizer assembly to perform its function. Therefore when the transmission is cold, or before it has reached operating temperature, quick, hard shifts should be avoided to prevent damage to the transmission.
Backlash noise is created when changing engine or driveline loading. This can occur when accelerating from a stop, coming to a stop, or applying and releasing the throttle (loading and unloading the driveline). This will vary based on vehicle type, build variations, driver input, vehicle loading, etc. and is created from the necessary clearance between all of the mating gears in the transmission, axle(s) and transfer case
Shift effort will vary among different style transmissions and synchronizer designs. Usually the more heavy duty the transmission, the higher the shift effort because of the increased mass of the components. Shift effort can also be higher in cold weather because the fluid will be thicker. Medium duty transmissions will not shift as quickly as a Corvette transmission. To reduce shift effort, do not attempt to rush the shift - allow the synchronizers to work as designed. Shifting harder will only increase the chance of rushing past the synchronizer leading to grinding while shifting.
Some light duty truck transmissions in 1st gear
(creeper-gear) and reverse gears in various transmissions, along with all gears in some medium duty transmissions, may be non-synchronized. This means there is not a mechanism to match input and output shaft
speeds to allow for a smooth shift. This function is left up to the driver. This can be noticed if a shift into 1st or reverse is attempted while the vehicle is rolling or before the input shaft
stops rotating leading to a gear grind. The grinding can be reduced by coming to a complete stop and pausing for a moment before shifting into the 1st or reverse gear. Some slight grinding can be expected. In medium duty non-synchronized transmissions, the driver must match input shaft (engine) speed to output shaft (driveshaft) speed with every shift. This can be accomplished by double clutching, or by using other methods. If the driver is not able to perform this function properly, there will be gear grinding with each improperly completed shift. Driver training may be required to correct this condition. Clutch
brakes are used in medium duty non-synchronized transmissions to allow a shift into gear at a stop. The clutch brake is used to stop the input shaft from spinning, allowing a shift into gear at a stop without grinding. The clutch brake is activated by pressing the clutch pedal all the way to the floor. When the clutch brake is used, it is possible to have a blocked shift with the vehicle stationary. If this occurs, engage the clutch slightly to rotate the input gear to allow the shift. The clutch brake is intended to only be used while at a stop. Care must be taken to not activate the clutch brake while shifting between gears. This could lead to excessive grinding or a blocked or missed shift.