I wish I could give a direct answer, but I can't.
I do know that RR temporarily mutes the audio when it receives the shutdown/power off/hibernate command from windows. It then is supposed to return the volume level back to normal before RR completely shuts down. It sounds like it is staying in that muted state and not returning the volume level to normal.
When you reboot / come out of standby, check the windows sound panel, and see if windows itself is muted. This is at least a place to start, and can hopefully narrow down the problem.