Hard disk activities in the evening without any access

My Cloud OS 3 My Cloud Mirror
1

Yesterday in the evening I recognized that the hard disks in my WDMyCloudMirror (Gen1) are working during a long time (hard disk sounds, Led flashing). But no device in my home had acess to that time.
What could cause these activities ?

  • chinese hackers who watch my holiday photos ?
  • Western Digital who watch my holiday photos ?
  • a self checking procedure in the System?

thanks for any help