I have posted something similar to this before but the problem hasn't been fixed.

I was in the middle of a minecraft game not doing anything special and all of a sudden the sound went out, so naturally I thought I somehow muted my speakers, that wasn't the case. Next i checked the minecraft sound levels and again that was not the problem either. So I quit minecraft and then shut down my computer for about a minute or so then rebooted, when I got back to minecraft the sound was still messed up. So like any other addicted minecraft player I kept playing, and over the course of about 2 weeks the sound would go in and out, so 1 game it would work and another game it wouldn't. I downloaded an audio mod not sure what it would do but that didn't help either. I have deleted my minecraft file (not just the bin file) like 2 or 3 times and my sound still doesn't work.

If anybody can help I would appreciate it, thank you. Also I am currently using minecraft 1.2.4 but my sound gave out when I was using 1.2.3 and just never fully returned.

If you need any other info just let me know and I will try to provide it. Thanks.