Oh yeah chimes could be fun. I agree that regular gun noises are pretty grating, especially free ones, so that might be a good alternative.
You don't need to add an option to take away the menus, just make it so that key presses place the turrets without having the menu open. It's better to have the player discover the faster way of operation rather than have to load the game with a setting enabled to see if they like it. It's like Photoshop, at first you use the GUI for everything, but then over time you start to take notice of the shortcuts written next to the things you do a lot and start to use those instead.
Managed to pass both the second and third levels, putting towers in their way is the way to go haha.