I’m using Android 2.3.3 (as about 50% of all Android users right now).
Right now the audio files are working. What I found out: 22 and 44kHz WAVE files work (1411 and 705kBit/s) but Audacity’s “mobile” format which only has 71kBit/s does NOT work.
Hmm I can check if I did that, maybe that caused this problem. At the moment I’m fine as long as I explicitly set the volume to 1 in the Sound element.