Been converting movies for about 6 months, using HB and MKVTools. Mainly 720p, converted with AC3 5.1 and AAC 2.0 audio tracks. Converted one this morning, (since upgrading to Lion and iTunes 10.4) and when I play the file in Quicktime the 5.1 track has a funny hiss. The 2.0 is fine. (This never used to happen with SL) Dropped file into iTunes and played it. Under the audio selection icon, the surround is greyed out and the stereo track is selected. Video plays but no sound at all. Gone back and checked and many of the files in iTunes play with no sound. These files play fine in VLC (both audio tracks) Can anyone else check and see if this is happening to them?