I have Fedora 17 KDE.
I used the gstreamer backend for Phonon, but it always makes my media players stop playing when moving to the next track and sometimes in the middle of playing a track. This is a known bug with the gstreamer backend that has been around since 2009 and also affects Ubuntu and seems to be unconnected to the media player that is used.
So I switched to the VLC backend which does work...
But every time I log in, all sound is highly distorted at first. When I play around with the settings for long enough, it sometimes just stops and I still haven't figured out what made it stop. But it's every time I start the computer.
Also, when I go to the configuration settings of phonon, it is always set to "HD-generic audio", which seems to be the troublemaker and I do get the distortion when making a speaker test. When I change to "SB Audigy", which is my sound card, the speaker test works. But every time I go back to the settings, it's reset as "HD-generic audio".
I do have onboard sound, but I had that disabled in bios months ago, since that made everything even more complicated.