Eu acho que você precisa ler isto
Para depurar ou resolver isso, tente as seguintes etapas:
remove all users (including user 1000) from the groups audio, pulse, pulse-access then reboot (no user needs to be in these groups for audio!).
Is pulseaudio running? Watch out for errors when running the following in a terminal:
pulseaudio
log in to the Guest account. Does your guest user have sound?
From your affected user account issue the following command in a terminal:
mv ~/.pulse/ ~/.pulse.bak/ ## removes erroneous user audio settings
pulseaudio -k ## restarts the sound server
Create a new test account to see if sound works there.
Do not run pulseaudio in system wide mode.
Is there an audio output sink at all? Read the output of the following command:
pacmd list-sinks
Remove all attached external sound devices including speakers, reboot and then plug them back in.
Further reading: Ubuntu Wiki: Audio