I read many topics about people having sound problems when playing a project in Kdenlive, typically in Ubuntu.
This happens when PulseAudio is bad configured and applies only for the preview, not playing the rendered project in an external player.
It seems it has something to do with the computer performance.
I found a solution 3 months ago, as reported on the Mantis:
To configure PulseAudio:
1) Edit the file /etc/pulse/daemon.conf:
sudo gedit /etc/pulse/daemon.conf
2) Find the following lines (usually at the bottom):
default-fragments = 8
default-fragment-size-msec = 10
I use those values for my sound card:
default-fragments = 20
default-fragment-size-msec = 2
Change them and try to find the best configuration for your system.
I only have a light crackling sound when the sound level gets high (when a sound volume in the video gets high). I would say that 95% of the problem is solved for me.
The solution was found on:
Hope this helps.
Note: to restart PulseAudio simply use "pulseaudio -k", it kills the process.