Speaker garbles on announcement

Hi List,

I have a Cyberdata Speaker that garbles audio when using a Playback or a Background.

HOWEVER!! - when I use Dial(SIP/100,20,M(play-the-file)) it plays fine. Is there something happening within asterisk that could be causing the playback to be garbled.

Calling from a SIP handset to the speaker also plays a clear sound.
The speaking in a conference room also plays aweful audio. Garbly sounds.

The only supported codecs are alaw/ulaw. Asterisk sends it only these codecs.

Anywhere for info would be great.