I have my kdl-52v5100 TV attached to a Sony str-dn1000 receiver via HDMI only. I use the TV as a monitor. I also have a Directv hd dvr attached to the receiver via HDMI. At times, the TV switches to TV speakers for no apparent reason. I switch it back in the menu to "audio system" and it stays there....until the next time. Once when this happened I noticed the receiver said "muting." I suspect the receiver is losing signal from the Directv receiver, but I don't lose video when this happens. Possibly HDMI? Thanks in advance for any input.