? about valves mounted on the tank in the trunk

I've heard that when you mount valves on the tank that it's really loud inside the car. I want my valves to be heard when I dump the car but I don't want them so loud that it hurt's my daughters ears bc she'll be in the back seat. If I used mufflers does that make them completly silent or can they still be heard outside the car. Also I have 1/2" valves and will be running 3/8" line, will mufflers slow them down or will i need reducers? One last question if I plumbed a 1/2" NPT to 1/4" line fitting to my dump valve and ran a 1/4 line out of a hole i drilled in the trunk floor will the noise be primarily outside now or still loud inside?