General Motors issued a number of technical service bulletins pertaining to clunking noises in the 2004 Chevrolet S10, but they also detailed several causes of clunking that Chevy considers normal and not a cause for alarm. However, clunking noises that are caused by excessive wear or component failure definitely raise concern, and they should be diagnosed and repaired before they cause further damage and possibly leave you stranded.
Gears within the drivetrain necessarily have a small gap between them to prevent premature wear and binding. This gap, or lash, can lead to a clunking noise as the drivetrain momentum changes during acceleration and deceleration. Models with automatic transmission can produce a clunk when shifting between Park, Drive and Reverse, and manual transmission models can produce the noise when dramatically changing the throttle setting with the transmission in gear. Four-wheel-drive models are more susceptible to normal gear-lash noises as they have more components and gears in the drivetrain. Since the lash is present by design, changing any individual component within the system will likely not result in an appreciable decrease in the noise.
The front wheel driveshafts can cause a clunk as the loads shift in the drivetrain by accelerating through a turn or accelerating from a coast. Wear in the driveshaft joints, seals and constant velocity joints can cause or exacerbate the noise, as can a loose or improperly torqued shaft-to-hub assembly nut. Check the torque on the nut and correct as necessary. If the condition persists, go ahead and check the other components, replacing any as needed. Noises only produced while coasting in neutral at 10 mph or operating in high gear can be attributed to bad universal joints in the main drive shaft, or a worn side gear counterbore. Check the universal joints, and if they are good, then inspect your counterbores.
Various components in the power steering system can also cause a clunking sound. Improper hose routing, low fluid, drive belt wear, drive pulley damage and power steering pump mounting bracket damage are all possible issues. Wear in the steering linkage, steering gear and intermediate shaft can cause a steering-related noise.
Noises that only occur with the transfer case engaged indicate a problem solely in the transfer case. Check the level and condition of the transfer case fluid, and service as necessary. If the noise persists, you may have a problem with one or more of the internal parts, including the slip-yoke splines, bushings, shafts, thrust washers and synchronizer hub. You must disassemble the transfer case in order to inspect and service these components. This may be beyond the shade-tree mechanic, as it will take a number of specialty tools, precision measuring instruments and experience to accomplish.
