Very frequently when switching from one channel to another the sound disappears on the new channel only. The only way to remedy this appears to be to continue to switch backwards and forwards between channels and eventually sound on the new channel is recovered, while sound on the original channel is not lost at all. This can happen randomly when switching to any channel. Rebooting has not helped. Neither has checking cables. Calls to Virgin end up automatically triggering an automatic system test which always reports that no problem is identified, when clearly there is a problem. Very frustrating. Assistance would be appreciated.