As others have said, the solution is disabling sound. Unfortunately, in recent Android Studio releases (I’m using 1.4) the option to disable sound has been removed from the GUI. To disable sound you can do it either by launching the emulator from the command line with the -noaudio flag, or by editing the AVD’s config file and setting the following parameters:
hw.audioInput=no
hw.audioOutput=no
On Linux, I found that file at ~/.android/avd/myAVD.avd/config.ini