Sounds a lot like CSCdv88847. You won't find this in CCO bug walker, and I am not sure why. To verify if it is reall CSCdv88847, check the event log for some MIU errors about WavSetVolume or WavSupportsVolume.
The workaround is to change the volume level for subscribers on the SA conversation page to "medium". Also make sure that all MM and VMO volume levels on playback controls are set to the middle, it's 5 I believe.
This defect is fixed in 3.0.4 and should be in all 3.1.x versions.
Steve Olivier
Software Engineer
Cisco Systems