Some audio question

Again playing a bit around with FCPX (and that bad documented XML) I found something strange.
As you can't match multi-mono tracks by timecode and the FCPx sync is not working, I thought it's a good idea to start over.
Made a new event, imported my audio, did this "some kind of sync" thing again and dropped it into the timeline/project. No sound - even though waveform and levels showed there is sound. Using the "open in timeline" I see all tracks and I can hear the sound. Even a single BWAV track file will be muted.
Importing an MP3 file and dropping it to the timeline/project works fine.

Did I miss something?

Andreas