I have been troubleshooting an issue with terminal services sound redirection for one of our customers for a while. Audio mapping was enabled and all of the GPOs had been checked and re-checked. Resultant set of policy showed everything should be working. The volume showed to be muted when looking at the sound settings through the control panel. You could unmute the sound and click apply and the "muted" check box would automatically re-check itself. All types of troubleshooting were done from DirectX diagnostics to a Microsoft PSS case. Skipping three days forward, the root cause was due to rdpclip.exe not running at user login. This process is started at each login subject to the existence of a registry key which was missing. [more]
The reason it was missing was due to a previous fix for performance issues. The registry key that was missing was HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\Wds\rdpwd:StartupPrograms --> rdpclip . I added it back and tested and sound redirection worked. However, now the performance issue is back. At login, there are several users who experience very high CPU usage for the rdpclip.exe process. Since rdpclip.exe is responsible for several types of RDP redirection, it was undesirable to remove the registry key again to fix the issue. I was able to determine through additional troubleshooting that audio mapping was the root cause. I can enable any type of redirection via terminal services redirection except audio mapping and the performance problem does not occur. At this time we still have not found a fix for the performance issue.