http://bugs.winehq.org/show_bug.cgi?id=15512
--- Comment #2 from Jason Rosenberg smitty_the_smith@yahoo.com 2008-11-15 06:06:50 --- (In reply to comment #1)
I had the same problem, but you could get around it. When you minimize or alt+tab, you have to show the desktop (ctrl+alt+d) then alt-tab back to WoW. That combo got the sound back for me. But after the 3.0.2 patch I don't have sound at all, but that is another issue.
WoW has a feature on the sound menu called "sound in backgroud" this was a work-around for me @ patch 2.4. let me know if it works for you.