I installed RetroPie from source last week and I have Genesis, Master System, PSX, SNES, NES, GB, GBC, PC Engine, and Sega CD all working great. They are fast, have sound and the controllers are working great.
GBA is running smoothly and works great with the controller, but there is no sound at all. I tried different sound frequencies in the settings (by pressing F10 in-game).
I have a Raspberry Pi B+ and have it going through HDMI.
I started up the Pi again this morning and lo and behold: GBA has no sound for all games.
I tried starting up a Sega Genesis game first and then all GBA roms have sound again. I shut down and restarted and tried GBA. No sound. Started an NES rom next and then came back to GBA again. Sound works for all roms again.
I shut down and power off the Pi every night. My best guess is that gPSP fails to start some sound-related process that every other emulator does start.