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Sound files are in /usr/share/sounds/deepin/stereo, you can simply rename or move them elsewhere.

Probably a little more advanced but I found several of the notification sounds just too loud on my laptop.

My solution was to install Audacity (audio file editor) and "normalized" the volume in several of the sound files to my liking and saved copies of them. I moved the original loud sounds to /usr/share/sounds/deepin/stereo/TooLoud and copied my new files to the original folder.

So I still have the notification sounds but they are just not so loud.  Incidentally, the sound files were .ogg files in 15.6 but were changed to .wav files in 15.7. Not sure why, but possibly .wav files require less CPU to play.