An upgrade to Moxi was installed today although I don't think that has anything to do with this. My wife turned the channel to 40(HGTV) and there was no volume. It was recording at the time so we watched the recording and it had sound through the whole show. After the show there was no sound on 40 again. My wife says it's happened before. Why would it have sound in the recording but not watching it live? That's the only channel it's happend on that I know of.
Edit to add that 40(HGTV) Has sound on the other TVs in the house that aren't connect to Moxi. So, it must be something with Moxi and that channel, since other channels work ok.