Yeah, my momentus xt (500gb) that's in the optibay slot tries to spin down and then immediately spins up again. I heard the momentus xt's had problems with spindowns. Seems that the original firmware was too aggressive with drive sleep and it caused spin-up lag quite often, but that the updated firmware is too conservative in drive sleep.
Anyway, I think it seems like the momentus is trying to spin down (usually after a while of reading an article or watching a youtube clip, so the platter wouldn't be used), but that there is some issue with the optibay and sleep that causes it to spin back up immediately. I have the "sleep drives when possible" box checked in energy savings.
Anyone have a fix?
Put the HDD in the HDD bay.