When I play audio files with the default application (totem), nothing can be heard (but the "disco effect" animations are active). Sound is not muted in totem and in fact is pushed up to the fullest. Opening the same sound file in audacity and playing it there works. There doesn't seem to be any place in totem where I could have misconfigured something. What could be wrong?
EDIT: The problem is apparently not related to audio file type. All the following files can be played from within audacity for example and are mute in totem:
$ file test* test.aac: MPEG ADTS, AAC, v4 LC, 44.1 kHz, stereo test.mp3: Audio file with ID3 version 2.2.0, contains: MPEG ADTS, layer III, v2, 80 kbps, 24 kHz, Monaural test.mpg: MPEG sequence, v1, system multiplex test.wma: Microsoft ASF