I think that if the log is separated into two sections, "regular" and "last turn only" with Ctrl-p and Alt-p respectively (or so), and by making instant-more and text-sounds .ini definable, this shouldn't be a problem at all. Also, if sound intensity is represented the way it seems to be used right now, two Barons won't produce *whine* *whine*, but one *whine* of a "louder" colour.
Just a question - how difficult would it be to add the monster sound texts directly to the map, just in eight general directions, and refreshed after every turn? This would eliminate the message overload problem mentioned by Blade.
I think that if a system like this is implemented, it should be used very carefully to prevent giving away too much information. It's almost Intuition(3), if you know where the sounds are coming from and how loud they are.
In any event, it should probably have one key used for each of the directions in a way similar to a message log, e.g. Ctrl-4 would give all sounds heard this turn from the west, Ctrl-9 would give those from the north-east, etc.
Writing this, I think that if it is implemented well and then used by many, there could be traits augmenting the chars "hearing".