Under KDE I can't get sound to work for more than about five seconds.

Going into the Phonon set up I pick a setting (eg digital stereo in and out) for the right soundcard, sounds works for about five seconds and then goes off. I pick another setting for that soundcard (eg digital stereo in and mono out) sound comes back, for another five seconds, and then goes away again.

I've removed the phonondevicesrc file in case previous installations are interfering. The file gets recreated, but sound is still flaky, as before.

This isn't the case under Gnome(3), sound works reliably there, although I have to have the audio setting dialogue onscreen for it to hold, at least initially.

I wouldn't be at all surprised if there was something wrong in my setup, but where do I look?

I'm running Fedora 15 64 bit.

TIA
Mark