How to disable event sounds in Plasma 5?

In recent Plasma 5, search "Audio Volume" in the application launcher and, under 'Applications' tab, disable 'Notification Sounds'.

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In some Plasma versions the above doesn't work, as I now see in Kubuntu 17.10. The Audio Volume tool looks different and notifications sounds is already muted.

To stop the volume scrolling sound etc in this case, I have unmuted, and moved the slider to zero, and muted again. Something is buggy here though, as the slider is in fact always stuck to zero, and only the mute/unmute button does the work.

In this case I have noticed that a different tool can be used: pavucontrol-qt:

After using this, the bug mentioned (slider stuck to zero in "Audio Volume") disappeared.