There is actually a mute button on the weapons screen. It is to the very far right of the Speed Level Build box and above the last "L" in Start LeveL" Thumbs up this comment so others can see and use!
this game DESPERATELY needs a mute option, and I wish we could continue to upgrade weapons like the homing gun etc. all in all it was kinda addicting and annoying at the same time. It'd be cool to see what gun I'm upgrading too.