this looks like a duplicate of #272321 which is currently assigned to the kernel team, but in the comments people have suggested that removing pulseaudio resolves the problem...
-- crackling sound when PCM muted https://bugs.launchpad.net/bugs/293405 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
