Disk Hibernation - again

[bitmap]

Have you checked scheduled tasks? There are some that might spin up the HDDs such as library scans, downloading subtitles or lyrics, keyframe extractor, chapter image extraction, trickplay, subtitle extraction. You could set these to fire once a day or only when the container starts. You'll sacrifice the functionality of all these tasks, but maybe that's not important to you. No guarantee this works, either. Some plugins can change behavior as well and -- as already stated -- hardware/OS may have some blame as well. You would have to figure out how to track HDD activity by process over time rather than at a point in time.