The jittery physics is definitely something I noticed, and as for now, I have two possible explanations.
Either I messed up some settings, or unity doesn't like, when there are physics objects of very different scales in one scene. Again- right now I have no idea- this kind of game was a first for me :)
As for the sound- omg, thank you for noticing. I have a feeling (and some comments from other jams) that suggest, the sounds in my previous games were mid at best. This time I spent more time on this part, and apparently people notice :D
Thanks for playing!