Activity light comes on when Drobo5N not being accessed

I have a Drobo5N with current software. A few times a day I see the Drobo with the activity light going and no one is accessing the Drobo at the time, no backups and no one is accessing music or pictures or any data on the Drobo. Why does the activity light come on? Any ideas??

Thanks
Jim Holloway[/font][/size]