fanart in background flickering

Hello there, I don't know, if this problem has been posted anywhere but I can't find help neither here nor through google.
Since quite a while the background of the my movie library and my music library is flickering crazy with fanarts in the background on every skin. I already reinstalled XBMC, deleted several files from my /userdata including /Database and /Thumbnails, uninstalled several addons including all with fanart and totally deselected fanart in every window but nothing helped so far.
My operating system is debian 6.0 squeeze.
Where should I look for the issue?