You need to provide video details
Exactly what are you editing, and what are your exact export settings?
Screen shots help
>Sony Handycam, HDV video
1st... your timeline has a red line over pretty much everything... which usually means you do not have a correct project setting
See 2nd post for picture of NEW ITEM process http://forums.adobe.com/thread/872666 to be sure your project and video match
2nd... I don't do H264 or Youtube, so have no idea if your output settings are good or bad
Are you able to export to anything else, and have good sound?
First off your using the Youtube preset.
Your source footage is 1920x1080i upper field first at 29.97 at 48kHz and your trying to output to 1280x720 44.1 kHz
You can modify the preset to match your source so you upload the full HD file by changing the Level setting to 4.1 that will be the start of a CUSTOM setting under the Preset. You can save it if you like it.
Then make sure to change the frame with and height to the original size of 1920x1080 and also change the Frame Rate to 29.97 also.
Under the audio tab make sure to change it to your source footage of 48kHz
See if that helps.
If its a hdv camera so should the sequence be: hdv 1080i30 which is 1440x1080 par 1,33. But I doubt its a hdv camera due to the 5.1 sound. HDV camera is usually stereo.
Use the HDTV720p29.97 for export and set MRQ on: all ready to go.