Have a similar Problem.
sounds only play like 2 or 3 times then go silent (nuke warning are complete silent ....) It is reproducable also in the Lobby, when you hover over the ready button (2-3 times you hear the little "ping" then nothing)
I have a onboard sound card (Realtek , Asus Maximus IX Hero) and a seprare Soundblaster USB G3 . you can't switch ingame between those two, because Java doens't like that. But even when i switch before the game, it's no different.
Restarts and new drivers already done.
some one got other ideas?