The problem occurs on my work computer, so it is a bit difficult for me to debug the issue.
However, I attach the list of my installed packages. I have done aptitude purge pulseaudio to prevent hear loss, but I could install it again and not wear the headphones to make some tests. The notification was a popup from amarok, explaining that if I close the main window, it will still be running in the tray area. I had done no configuration to notifications or audio. I had installed kde-full, and configured themes, keyboard and other programs.
pkglist.gz
Description: GNU Zip compressed data
