Hi mainframe,
you're obviously using a sound transducer instead of a selfcontained buzzer.
Just for your information: A selfcontained buzzer generates an audible signal when connected to a DC power source.
If you use a sound transducer you'll have to make the sound signal yourself, which you can do using a dual timer chip, one wired as monostable and the other as astable multivibrator.
The monostable will trigger the astable (set to the desired audio frequency) to have the piezo transducer sound at your desired frequency and time.
The monostable I suggested is a retriggerable one, meaning it will keep the output high as long as the button is depressed + time delay set by the timing RC combination.
Boncuk