Caviar Black can't go sleep on macbook pro

I got WD Caviar Black   WD7500BPKT i nstalled in my macbook pro 13 (mc375) additionally to other SSD drive.

I faced the problem that WD drive is always spinning. I always hear the noise from the drive.

In my mac os x setting it is makred to “put the hard disk to sleep”. But this option doesn’t work.

On this WD drive I store only video files, so it should be accessed and “turned on” only when I want to open some video. But it spins all the time.

Coould it be some conflicts between WD drive and Mac os x setting for power saving? How I can check it. Thanks to all.

I think WD could provide you with a better answer to your computer issue. You can either call them or email them. 

also, have you checked your power settings for when the drives are supposed to power down?