Eu tive o mesmo problema, mas para o Spotify.
Pesquisando, encontrei o seguinte: link
Essentially PulseAudio is deliberately delaying global volume changes. This can be changed:
- Get a root terminal and edit /etc/pulse/daemon.conf.
- Find the setting "enable-deferred-volume", remove the semicolon at the start of the line if is commented out and set its value to "no"
- This will enable instant global volume changes
Get a terminal with your normal user, restart the PulseAudio daemon:
pulseaudio -k && pulseaudio --start
The man page warns about sound glitches that might occur when switching off deferred volume changes. If you experience this, switch it back on and adjust the delay settings to lower values until it suits you.