My DS uses the acapella choice, I think. The dark green one that can be taken apart. Sometimes the piece inside won't flutter, the air just blows right through. There are no broken pieces, and I washed it, soaked it in vinegar, and then boiled it in case it was the chalky residue from boiling that caused it. I keep opening it and fiddling with the flutter part but it's just not wokring this time. This happens to us a lot but I can't get it right this time.