The sound just goes, like someone has muted the tv. It happens randomly. Sometimes just changing the channel brings it back. Other times we have to reboot the box. We also randomly get sound loss on recordings. The sound will go if we try to fast-forward through a recording. The only way to get it back is to stop the recording and start it from the beginning.
Re the overheating issue - just the one box and this is the first time it's happened.
We would like to take a look into this further for you. To do this, we would need some more details from you. I will send you a PM requesting the details we need, if you can reply to this with the details, we will be more than happy to help.