Crackling and delayed sound after upgrading to 18.04
I had the same problem. It seems related to speech-dispatcher (some text-to-speech utility).
try :
killall speech-dispatcher
If the sound comes back to normal you can remove it completely (if you don't need it) with :
sudo apt-get remove speech-dispatcher
I had the same issue and killing pulseaudio fixed it for me. I'm not sure why it would get into a bad state, but restarting pulseaudio might be something to try.
Try
killall pulseaudio