HDDs not spinning down when idle

I have a recently built computer. This system has six drives, five of which are HDDs. The system drive is an SSD. Two of the HDDs are primary drives: one is for programs (mainly games) and the other is for media (videos, pictures, documents). The remaining three drives are backups, one for each drive. The issue is those remaining three drives don't spin down, even though they should be idle 23 hours of the day. Nothing should be accessing those drives.

The only reason this is an issue is that with five HDDs constantly spinning, my computer is fairly loud. I built it to be silent, and without them spinning it virtually is, with the exception of the PSU fan which produces little noise. I'm considering buying external enclosures for all of them, but I'd like to avoid this. My previous system which was running Windows 7 had no problem spinning down all idle HDDs. Any suggestions?

Anyone?