This update (or this) eliminates the noise made by the optical disk drive during system startup and wake from sleep on MacBook (Pro) computers. When installation is complete, please run Software Update again, and install SuperDrive Firmware Update 3.0.

Also ich höre mein SuperDrive (laut System-Profiler ein “HL-DT-ST DVDRW GS21N”, nach dem Update Version SA18) zumindest beim Start immer noch.