Why Does my HDD Spin When My SSD is my Boot Drive?

i have 128gb crucial m4 in main bay of 2011 13" mbp.
have stock 320gb hdd in optibay. boot files/applications/data copied carbon copy cloner ssd hdd.

m4 has been set boot drive, however, while using laptop, hdd still seems spin. example, when quit application after leaving mbp idle while, hdd needs spin before quits. i'm not sure why happening, considering on ssd.

suggestions?

 

i've got same set dont hear hdd spin. did clean install though if matters.

 

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