A few things,
Check that it still has all it's feet.
Certain CDs with "heavy" labels will cause the drive to spin inconsistenly.
CDs that were burned at high speeds will spin at high speeds. (I think)
I've had it happen only once to mine, I tried to install W2K Pro from CD using bochs. I let it run during the night and my TiBook vibrated off the table. Otherwise my CD Drive is pretty quiet but I've only used old software and DVDs with it.