Sound client broken?

Sometimes when I start a game, there's no sound. It's like the sound client for the game doesn't open, and I have to leave and rejoin to get sound.

If I check the volume mixer on my computer while the game is running when this happens, there is no "League of Legends" icon showing that it's even able to make sound. It gets annoying, because I'm starting to get warnings for leaving to many times because I need sound.