I did have an extensive search for an issue like this but could not find one.
Basically in the 15w43a, b and c update (when subtitles were added) and the following snapshots sound has not worked on my Minecraft client. It only occurs in these updates and I have tried to reset the Minecraft sound using F3 + t to reset resource pack but that does not work (I should also add I am using the default resource pack). My sounds definitely are not muted and the music is not working either. Subtitles also don't work for some reason which could be related to this since no sound=no subtitles or it could just be a whole separate bug. I have tried reinstalling Minecraft using the msi.installer but that has not seemed to have worked either. I do not think this is an anti virus issue either. I turned my software off and the sounds still did not work. For me personally the options_old.txt did not work either (but it is worth a try.).
This bug is still prominent in the latest snapshot 15w47b (which I believe made changes to sounds in game).