No sound/music - Found the cause

[Sevenless]

You'll get no sound/music in enders if you muted sound in the traditional client before switching over. Doesn't matter what you set their sound options too. Probably applies to all modded clients. Will also be posting this in enders client thread, but it's a gameplay issue since almost no one uses vanilla client imo.

[mvgulik]

Things are a little different if I remember correct ...

Something to do with two minor bug's working together to confuse you. (that's why including what exactly you did can be so much more informative ... in case your concluding is wrong.)
---
aha, found it. viewtopic.php?f=2&t=9835&hilit=+sound#p107422
(and its passed on to the custom clients of course.)