The Cisco Unity comfort noise setting causes the Cisco IP phone to generate audible white noise.
Comfort noise controls how much background noise a Cisco IP phone generates when there is no audio from Cisco Unity, for example, during a transfer or between system prompts.
You should reduce the volume level of the comfort noise. Check the comfort noise registry setting.
For more information, refer to the Comfort Noise section of the Audio Quality chapter from Cisco Unity Troubleshooting Guide, Release .