I looked through the manuals and couldn't find anything for turning that off.
There are some options for changing the greetings when a call is forwarded into VM but not when being xferred.
Here are some options:
1- someone here may have the time to find the actual file in the system and explain how to delete it or change it to silence. Really not something I would suggest in a production system. (although obviously I just did suggest it.)
2- Instead of using VM to do this, switch to trying ACD with the interflow options. An ACD path with "ACD Path Interflow Dialing List" will do this for you.
Ralph