To be completely fair to you, I did notice that this audio glitch phenomenon happened to me while trying a lot of other in-browser games, so I think this might be less of an actual volume mix or audio issue, and more of an optimisation issue? I don't exactly know what it is, but you're definitely not the only ones this has done this to me with.
I'm not sure if you guys will keep at it after the game jam but would love to see updates personally!!