I just upgraded to RetroArch 1.8.4, and while it seems to be an improvement over the past several versions I’ve tried, it still has a couple issues. The audio from Beetle PSX HW echos (I tested a game on Beetle GBA, and it has a similar issue). Also, during my first session, it didn’t have much of any speed issues, but during subsequent sessions, it did run a bit slowly. The audio drivers wasapi, dsound, and openal all seem to have audio/speed issues (wasapi is the driver that has the above described echo issue; dsound and openal have issues with audio static). As for the xaudio driver, while it starts out working absolutely perfectly, loud static will cut in either after certain events during gameplay, or, for some games, after exiting the RetroArch menu.
What FPS are you getting when this Happens?
Im not familiar with that particular GBA core I use a different one but I do remember using a GBA emulator back in the day that had bad sound unless you ran it with a bios. I dont know if that would help at all but I thought it might be worth a mention.
The Legend of Dragoon: 14.99 FPS
Spyro the Dragon: 29.97 FPS
Gran Turismo: 29.97 FPS