DailyTech have spotted WD's 36GB and 74GB Raptor hard drives to have just recently been given a silent update with double the cache (from 8MB to 16MB) and also native command queuing (a change from the older Tagged Command Queuing method).
Among the performance updates are increases in 'Buffer To Disk' sustained transfer rates of 84MB/sec up from the previous models' 72MB/sec as well as lower overall average seek times. The updated 36GB and 74GB Raptor models are also 3 dBA quieter in the idle state. However, both drives still carry a SATA 1.5Gbps throughput rating.
These updated models are not shipping yet, but retails tell us the drives should appear within the next few days.