I have tried to transfer .mpg files from my PC to Tivos using Tivo Desktop. The transfer to a series 2 unit works fine but trying to transfer the same files to an HD unit doesn't have any audio. I can transfer the files from the Series 2 (where they are OK) to the HD unit and again no audio. If I just transfer Tivo recording from the Series 2 to the HD unit, everything is OK. I don't understand why the files would play on the series 2 but not on the HD.