I had some problem with crackling sound on my system that comes and goes. I just figured out that the source of this problem is most likely speech-dispatcher. I googled it, and others had the same problem with this. Unfortunate, there's lots of dependencies that rely on it so there's no way to completely remove it.
But you can disable it from starting all together if you uncomment "# DisableAutoSpawn" in /etc/speech-dispatcher/speechd.conf and /usr/share/speech-dispatcher/conf/speechd.conf. This seems to fix my problem.
-- Mike