In the 90s, and up until cell phone cameras were a big thing, I remember some family members having cameras with rather large flash modules on top and it would make a weird noise once the flash goes off after taking a picture. Some smaller flash capable cameras would make the sound also.
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Camera flashes work by dumping a lot of energy quickly in a gas discharge tube, creating a very bright flash of light that lasts 1 ms or so. This energy gets temporarily stored in a high-ish voltage capacitor (400V or so), so the voltage from the battery needs to be increased (by means of a boost circuitry) that generally works via an inductor or transformer pulsed at few kHz, in the audible range, causing that characteristic chirping whine.
Generally, the capacitor would get charged at turn-on (for an external flash) or when selecting the flash mode (for a built-in flash), and immediately replenished after a shot (so, those would be the time you would hear the whine). If you really put your attention to it, you would also hear some infrequent, quick bursts of that whine in between shots as well, as the capacitor is generally slowly discharged via a resistor (for safety, as the energy could otherwise remain stored for a long while), and would need a periodic “top-up”.
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