Sound effects and music / ambiance will be completely reworked at a later point in time.
As for it being quiet, I'm not sure if you noticed the audio levels can be increased to 200% in the options menu but that should let you make it a bit less quiet.
Also I kinda realized just now that this is a bit weird so I will put this on the list and see if I can improve on this.
Do you mean inventory items as the ones on the in-game HUD or do you mean the upgrade list menu?
In any case, I'll add both to the list and see if I can improve upon this.
Anyway, thanks a lot for the feedback, hopefully I can improve on what you said. :)