Defrag disabled, but still tries to run when system idle

Despite having disabled the defrag [I only manually run same after every windows update] it still tries to 'optimize the drive' when the system is idle. Is there any way to override this? It's only started doing this again after I installed the huge rollup update earlier this week.

Have you disabled it in the task scheduler? Start - Run - Taskschd.msc
Go to: Task Scheduler\Task Scheduler Library\Microsoft\Windows\Defrag

Right click on the task to disable it, not sure what it is called, I have removed it.

Also, there might an entry at: Task Scheduler Library\Microsoft\Windows\Maintenance

How do you know its defrag that is running ? I have Windows defrag turned off too and haven't noticed any change in behaviour. Once a day a "maintenance" routine runs, that is accessible via the action centre and can be run on demand if needed. I've never looked into all that that does, but as to noticing more activity or anything, can't say that I have.

Resource Monitor under the Task Manager Performance Monitor shows which processes are using up the disk. This slows down my machine, and makes it unusable until the defrag and Norton's backup 360 is complete.