Hey, thank you for putting in all that thought into a little something I made. It's great to see it generate so much enthusiasm. :-)
About the ending, I hesitate on commenting too much about it. I found that reading players' interpretation of it was very interesting and revealed aspects of the game to even myself. I have a 'canonical' meaning to it (I always have, for all of my projects), but people's point of view about it reveals stuff about my own process and ideas, and I kinda like it.
I guess the one hint I could give about what I intended to do with the ending is that, yes, it is about the war. I suppose this much was obvious. The protagonist has been part of the war effort happening before the game, which explains in part why they are 'good' at 'repairing' heavy machinery.
Sound wise, it's a result of a few processes. I am very picky about the sounds I use. Even good sound libraries have sometimes subpar sounds, so it really comes down to being patient and look for the right sound (prioritizing the quality of the recording). If I can't find a quality sound for what I am looking for, I look for alternate sounds that might evoke the original intention (like using a washing machine or creaking wood floor sounds for some of the machines heard in please). I would recommend my personal go-to soundbank Zapsplat for audio work, it's free (they recently changed their free policy for .mp3 files only, which is fine by me. You've heard mostly .mp3 sound files converted to .wav in please and it did a decent job) and they have a good selection.
Some sounds I can't find online I record on my own. I have an old Zoom H2 recorder at home (a carryover from my radio reporting days) and it is great for recording all sorts of things, in surprisingly high quality. For example, the groaning in the main power machine was recording by myself while laying down in bed under the covers (to muffle the echoes). So yeah, a big part of the creepiness of the groans is my performance, I guess? I really played around with my head, jaw and throat positioning, to get an uneven, surreal voice, to the point where it almost made me sick. I stopped recording voices earlier than I thought because I couldn't go on.
Last thing about sound design : never use the sound as-is. Always modify it / equalize it first. Make it your own. It'll unify the soundscape, give a single personality to the whole project. Add a slight reverb, down/up-pitch it, mix two sounds together (or three! or four sounds!), play with the volume, add a filter to make it sound like it's coming through a wall, etc. For example, my voice performance was tweaked, down-pitched, and mixed with machine loops to the point where it became unintelligible. I wanted players to have a double-take moment where they went 'wait, is that a voice?'. Each time you go back down to the machine it's a new voice sample loop that is used, evolving from just groans to clearer pleas.
I use a mix of Audacity, Sony Soundforge and Ableton Live for sound editing (yeah, Live is a DAW, not an audio editing software, but some of its plugins and its warping capabilities are top-notch).
Some indie creators stick to the low-poly aesthetics in visuals and low-fi slightly-bit-crushed sounds to really go deeper into the 32bit feel. I can appreciate the results, but I believe high-quality audio over the low-poly look fits just as well together and helps with the interpretation of the visual elements. To my personal tastes, immersion starts with the soundscape.