Often when my box boots there's no sound. This can be fixed by entering the box into stand by and then waking it up, though sometimes it requires a full power down and on cycle/restart.
Sound also drops on channel changes which needs another channel switch to fix and sometimes several changes. At times i need to again power down the box then up again. That's not as frequent but it does happen.
Forwarding and rewinding both recordings and live TV causes sound drops too. I then have to stop the playback and resume or if on live TV change channels.
It's getting more frequent and increasingly annoying.