This appears to be a secret song for Marathon Trojan.
It can be found in a snd resource in the Trojan Manual. In Classic, after pasting the file to Scrapbook, then dragging it to the desktop, it was converted to .aiff format with SoundApp.
Thanks to GrimCleaver for teaching me this technique. :)
The song itself is 41 seconds long, and it ends rather abruptly. This is probably because it isn't the full song. It is still enjoyable.