iMac 5k, 10.11.3, Time Machine Off, TimeMachineEditor I have a USB HDD dedicated only for my backups, nothing else. TimeMachineEditor has been set to: Interval, back up once per day, do not back up between 11pm and 8am. Time Machine is set to OFF (I assume the TimeMachineEditor does that). For some reason OSX constantly accesses the Backup HDD. What could be the reason? Thanks.