I don't know if it only happens to me, but in this game, when you hit any enemy, you feel a slight pop in the sound. I don't know how to explain it, but that doesn't happen in Mame. It's very small, but there it is.
It'll be a matter of Hz? Because according to mame the game goes to "57.430000 Hz", and in FBN it seems to go to "60 Hz" since the scroll is quite smooth...
Greetings!