Does the noise occur immediately after you turn your computer on? If so, the only way to disable it will be to remove power from the drive by detaching it from the logic board. No .kexts have been loaded at that point in the boot cycle, so if this is the case, removing any kernel extension won't have any effect. If it happens randomly only once the machine is up and running, then removing a .kext might be your answer, but I wouldn't put money on it--someone else will need to enlighten us about that.
I have a similar MacBook, and the only time I ever hear the optical drive do anything outside of when I'm trying to use it is at boot, or when bringing the machine out of sleep. It shouldn't be spinning unless you have a disk in there. Perhaps the drive thinks there's a disk present, in which case blowing out the slot with compressed air might be of help.
Your only option may be disconnecting the drive. The machine is already out of warrantee, so you won't need to worry about voiding it, and according to the iFixit for what I believe is your machine, the repair doesn't look too terrible. You'd only need to go down to step 11, though there are some Torx screws involved.
Anyway, I'll be interested to hear if @John's kext solution works for you.