Could you please clarify if you're trying to capture the playback sound from the remote Host machine's sound card (e.g. music, video, some system sounds, etc.) or the microphone's input? Also, could you please let us know if you have multiple audio devices set up on the remote Host machine?
In addition, please try updating Remote Utilities to the most recent version - 6.12 Beta 1 and see if the issue still persists. The 6.12 Beta 1 version is available for the download on this page. When updating Remote Utilities, please make sure that you update both Viewer and Host as the version mismatch might lead to performance issues and some features not working.