Hi, it also happens to me. I'm also using the lastest version.
Menu runs at 50 fps (PAL) but background music is very sow.
Games runs at 30 or 30.1 fps.
In Recalbox forums they said it is fixed commenting audio_pwm_mode=2 line, but I doesn't help with Batocera.
Also, the volume is very low. Is it normal with RCA or only happens also with lastest version?