I noticed there were a lot of seemingly unnecessary internat structures. I used meshlab to remove them and my slicer likes it a lot better--infill and perimeters work like they should.
It also seem the whistle could be a lot shorter. There's a lot of wasted space beyond the resonant chambers. Any reason you don't change the lanyard hole to be vertical and put it right after the resonant chambers? That would make the model print faster and look better.
One thing I needed to do was to rotate the model so that the first bridging layer above the open chambers was full length front to back. Side to side didn't bridge well and left a lot of hanging bridges.
Not a bad model, thanks!