Or, for an alternate title, “How to manually set a speed on your optical drive”.
I have an aging Thinkpad T61 (maybe the last one to have shipped to North America with SuSe Linux pre-installed!), and it has an optical drive that creates quite a noise and serious vibrations when running at full tilt. So if you need to do something with your optical drive want it to run nice and quiet in Linux, try using hdparm:
hdparm -E4 /dev/sr0
The -E is for the speed. So -E4 is 4x. -E8 is 8x. Etc. The last is your device which in all recent Linux versions starts with /dev/sr0 (then /dev/sr1 and so on).