Modify the prompt tone or volume change-display error

[Liang-zy]

Version: 20.04LTS
Test environment: ThinkPad X1
Test steps:

1. Open the Control Panel-Device-Sound
2. Modify the prompt sound and volume change
   Expected results:
   Step 1 The control panel is normal
   Step 2 The modification prompt is normal
   actual results:
   Step 1 No exception
   Step 2 When the prompt tone is modified or the volume is changed, the three prompt sounds of ‘not connected’, ‘system log’, and ‘application error’ are displayed, showing an error, and there is no sound after modification