This is my redesign of the famous whistle. I made the pea more round and the body a bit thinner. I also put the pea where it is easier to break off. It now makes the staccato whistle sound.
Print with no extra shells and 100% infill. If your walls are not absolutely solid it will not work. If it fails, rub some acetone on the flat faces and let dry. This normally fixes it. It is also good to calibrate the infill and bridging settings as it wont work if they are not good.