I have the same issue on Xubuntu 18.04 and Debian Stretch. It occurs on a fresh install while watching a video in Firefox. Restarting Pulseaudio does fix the issue for me as well.
I observed that when the problem occurs, I can see multiple instances of speech-dispatcher in Pavucontrol. Whenever I select a different output device for all of them, the crackling disappears. If one of them has the same output device selected as Firefox, the crackling comes back.
I could fix the issue by uncommenting the last line (DisableAutoSpawn) in /etc/speech-dispatcher/speechd.conf.
I have the same issue on Xubuntu 18.04 and Debian Stretch. It occurs on a fresh install while watching a video in Firefox. Restarting Pulseaudio does fix the issue for me as well.
I observed that when the problem occurs, I can see multiple instances of speech-dispatcher in Pavucontrol. Whenever I select a different output device for all of them, the crackling disappears. If one of them has the same output device selected as Firefox, the crackling comes back.
I could fix the issue by uncommenting the last line (DisableAutoSpawn) in /etc/speech- dispatcher/ speechd. conf.
I hope it might help.
My system:
Xubuntu 18.04
CPU: Intel i3-4160
Motherboard: Gigabyte H97-D3HM
GPU: Nvidia GTX 1060 3GB