Hello, I have never heard about this BAS but I found it interesting and did some research. If I'm wrong please correct me.
I read that the BAS is some junction of the device software and the BB server, not something that we can install or uninstall. BlackBerry Attachment Service
If you haven't change (updated/downgraded) your OS, I think you should:
1. Check the size for the wav files. Maybe you did preview smaller files.
2. Consult with your server administration if they have changed the bit-rate of the files.
Please keep us informed on your resolution.