Thanks to Raydon, af123 and others I've downloaded a decrypted HiDef file onto my Windows XP PC. But when playing this file with both VLC and XBMC the sound "pulses" getting noticeably louder and quieter. The picture seems fine. I tried using m2tstots on the file to see if that had any affect but playback of the resulting file is exactly the same as before. Any ideas? I don't have a hi-spec graphics card but I do have a 4-core machine and it doesn't appear to be a "lack of processing power" issue. I've also hunted around for options on my sound card and in VLC & XBMC but don't see any that have any affect. Could this be something odd from the 5.1 audio track that I need to fix? I seem to remember reading a post somewhere about odd sound issues but the only ones I can find seem to be about issues playing back on the FOX-HDR. FWIW, SD output plays fine using VLC, XBMC and WMP. Thanks Papadeltasierra.