I've just google for this issue and found that apple state this is a normal behavior just as it is actually powering up the harddisk, fan so as the dvd drive.
So, does that makes my quiet 13'' mbp abnormal?
I've also read in some topics that some successfully stop the auto dvd startup by setting a region code.
unfortunately, that didn't work for my mbp.
So, does anyone have a quiet dvd drive for your 13'' mbp?