I went to a pet store and bought a “silent whistle” - it has a screw in piece at the bottom. The instructions say to blow it near your sleeping dog and untwist the screw in part until the dog wakes up and looks at you (and then you’ve found the setting you should use to train him).
Except… it makes plenty of noise in a human-audible tone at any screw in position. It’s not silent at all. Am I doing something wrong? Is it defective? Is a small amount of sound energy bleeding through to the human-audible range so that it’s mildly loud in that range but very loud in an ultrasonic range?