I can hear the high pitch sound of the recharging capacitor. Neither my mom nor dad can hear it, but my brother and I can. It is likely that the people designing these products have fully developed ears and cannot hear it either. Design flaw? Sounds too cool to be a design flaw
. Once it reaches full charge, the high pitch sound stays on one tone and doesn't stop until I turn it off or trigger the flash, in which case it makes the sound again. It sounds even louder and more distinctive with the rechargeables (at the moment I'm using alkaline 1.5v).