After testing new Kubuntu on my laptop I have noticed this annoying click just after sound is played. It seems that soundcard goes to sleep if it is not used to save power. To leave sound card enabled and to get rid of this sound you need to edit alsa-base.conf file.
sudo mcedit /etc/modprobe.d/alsa-base.conf
find the line with
options snd-hda-intel power_save=10 power_save_controller=N
N=number of seconds before alsa goes to sleep state. Change this value to 0 or put # in front of this line.