Yepper; I dealt with this problem on Williams sound speech boards.
The problem is your MC3417L.
There are 2 versions of these. (Unfortunately).
It took me about the same amount of time to figure out what the heck was going on.
Speech section from a Black Knight pin would not reproduce speech.
I put in Firepower speech EPROMs and voila............ speech like there's no tomorrow.
Speech IC4 on the speech board for FirePower is unused, but populated for Black Knight.
So, I had a bunch of MC3417L chips and started swapping these until all of a sudden Black Knight started talking.
What causes it, I don't know. Must be something internal of the 3417.
But I bought some extra of these chips and filtered out the ones that only work for speech in Black Knight.
I recommend you do he same, buy a bunch of these (EBay) and find those who make all your sounds work with ALL eprom locations populated.
The sound itself has nothing to do with it; it is the amount of (speech) EPROMs used in a game.