I have a VIZIO LED/LCD VF551XVT hooked up to a motorola HD DVR with a HDMI cable. When I switch from standard Def to High Def channels I lose the sound. If I turn the TV off/on the sound returns but if I flip HD channels after that the sound will go out agian after 4-5 channels. Never loses sound on SD just on HD channels. Not the same channels, no pattern present appears to be random.Have tried new HDMI cable, returned TV and got new one! Tried all the HDMI ports. Nothing helps. Component cable hook ups works, no problems...but lower quality picture. Have tried every setting on TV and cable box and talks with several techs. No one has an answer!

I have the same set, same problem with one of my MOTOROLA boxes, but not with another. I have a SONY TV that works fine with this new MOTO box, but the new VIZIO does not. The audio is coming through the HDMI cable just fine, and the fact that it works when you cycle power on your TV means it's the SYNC between the TV and the BOX. I have the identical problem and am taking back the MOTO box for another one. I spoke to VIZIO for about 45 minutes trying different things. They think it's the MOTOROLA box, COX (my cable company) thinks it's this particular box, who knows.

I have this same problem, when I turn on the TV there is no sound. I have cycled through HDMI and off air signal and comp 1, all with no sound. The only way I can get it back is to go in to the menu and change the sound to fixed from variable, then it will pop back on. Since the lack off sound happens with digital tuner on local channel I know it is the TV and not my Direct TV box.

A LOT of HDMI formats DO NOT push Audio through the HDMI, they only use it for Video, so you must run your sound separate usually via the RED & WHITE Audio out jacks.