To expand on the source of noise and possible solutions ... Regardless of price, multilayer ceramic capacitors are piezoelectric - meaning they physically vibr

To expand on the source of noise and possible solutions ... Regardless of price, multilayer ceramic capacitors are piezoelectric - meaning they physically vibrate. Inductors and transformers are electromagnets powerful enough to noticeably vibrate and move themselves. In fact, if you test them during assembly before taping them, the two halves of the ferrite core will snap together like magnets. Most noise comes instead from the windings, but that gives you an idea of their physical power. The biggest winding in an induction cooktop is the induction coil itself. The reason you hear them is because they're being used at audio frequencies. Considerate designers choose higher switching frequencies above what humans and household pets can hear. Induction cooktops are kind of a special case where it's tempting to dip into the audible frequencies. Frequency choice alone doesn't eliminate all noise, so there are other mitigations like materials selection and assembly, to name a couple. Overall, it's largely due to being cheap about the design and manufacturing processes.