I jumped so many times when playtesting this! Either because a zombie managed to creep up behind me, or the Jim Reaper, or... Well, I won't spoil anything else that's in it. :p
In the options menu there should be tabs in the top left, one of them is for Audio and you should be able to adjust the music slider there, did that not show up? (The music doesn't loop because it was the last thing we put in and apparently we missed a tickbox when exporting so I think there's only around 30 seconds of music unfortunately.)
I'm glad that the game made you smile, thank you for playing!