I'm making some ultrasonic 'buzzers'. It is essentially a pzt ring that is glued with an epoxy resin to a thin steel diaphragm. I'm sure most of you have seen the audible buzzers you find in alarm bells, toys and the like, and this is similar. My buzzer is ultrasonic and operates at around 40KHz for resonance so theoretically it should be silent to the human ear, but there is a very noticeable audible ticking that I need to get rid of. What can you suggest?