I've just begun playing BG1, and many of the sound effects are wrong or missing compared to the original interpreter. Most obviously, the ambient birdsong and murmur of voices in the starting area of Candlekeep are missing. Also, no cows mooing or gulls crying. The footsteps of my character seems out sync, more like a slow, syncopated drum than actual footsteps, and they will continue even though I have stopped walking. The sound effect of a door opening and closing will occur for no reason (is this instead of the cows or gulls?) . The "scroll being unravelled" sound when getting tool tips is missing, and instead of the "click-clock" of trying to open a closed container, there is a voice saying, "This container is locked".
If I save my game with GemRB and then open it with the original interpreter, the ambient birdsong will be missing there too.
GemRB compiled from Git repository source July 19th, 2012. GUI enhancements off.
Mac OS X 10.7.4. Unpatched BG1 from GoG.