Stop sounds when deleting files etc

I have set the “Sound theme” to “No sounds”, yet I still hear those irritating sound when deleting files.

You could try installing dconf-editor (if not already installed).
:~ sudo apt install dconf-editor

Open dconf-editor. Browse to
org/gnome/desktop/sound
On the right, unclick event-sounds.

Unfortunately it did not work.

Sound Preferences

Set alert volume to mute.

im glad you found a fix