Why would a LED torch chirr?
Step down regulators going to step-up regulators are notorious for acoustic and electrical noise.
I had one that was chaos or white noise and the ferromagnetic noise was so loud from the little SMD inductor in a noisy lab, it sounds like a water faucet.
The cure was a low ESR e-cap like the low ESR (&lt;50 mOhm) of a Li Ion battery. But beware not to make it too big as the surge current and overshoot of the buck can be really bad.