Printed the file with "fixed" in the title - but it doesn't make much of a sound. Maybe it's in the settings? I had this on a bigger printer, with an 0.4 nozzle... Suggestions, anyone? :-)
A while ago, I printed this other model: https://www.thingiverse.com/make:174843 - made by lmschupbach. That actually did work just fine, but was on a smaller printer with an 0.35 nozzle.
Edit: I used a file to sharpen the indicated corners shomewhat (see whistle_mod.png) - this did increase the sound quite a bit, but not to the level that I would expect from the description.