And testing. There's two implementations.
This one written completely by AdamP. From a coding perspective it is very basic, it's just KeeperFX playing another OGG file on top of the regular music and sounds. The real work is the ogg files AdamP created for this, where the original game played a fixed sequence of sounds (lost to time, except for the first 3 minutes) to imitate semi-random intervals, AdamP recreated it mostly from memory and by extrapolating the existing sequence with the desire to include all possible sound-transmutations. For this to work the game has to be bundled with a set of large OGG files.
This is the second one. This one uses the exact wave-files extracted from the game, but without a pre-baked sequence. It simply plays a random sound after a random amount of time (which averages out to about 25 seconds) with a random transmutation. This just marginally increases the size of the game but requires tweaking to get the sounds to sound just like they did in the original game. And because I wrote the code for it, while not being a coder at all, I want somebody who is to look over it as well.
That said, I played a few maps with it recently to get a feel for how it actually works in game and I got to say I like it. I completely forgot it from the original game, and the background sounds serve no gameplay function, but it does exactly what it is supposed to do, it adds to the atmosphere.