Found this really loud whistle from carlr3 (https://www.thingiverse.com/thing:5895673) and it's a really well made model. Added some text / logo to it to make it nice and shiny for protests.
It's printing quite well with no infill. It's designed to work without MMU but with a filament change mid print. Worked fine for me however please double check the color changes before printing.
You need to loosen the ball inside the whistle with a small screwdriver. Don't be shy since this needs some force.
The author remixed this model.
text / logo added