Thank you for your reply.
I am using Windows 10.
I want to notice when a error occurs, so I do not want to turn off the sound.
Changing the sound is a good idea.
I changed the sound and noticed.
When I open the SoundMixer at the moment I hear the Notepad ++ error tone, I see the Notepad ++ volume settings.
solved. Thank you very much.
—The process of changing the sound—
Sound used by Notepad ++
C:\Windows\Media\Windows Background.wav
↓
This file is protected by the “TrustedInstaller” permission.
File Properties → Security → Change Owner and Access
↓
Rename and save your favorite sound with the file name “Windows Background.wav”.