Most inverters sing a bit within certain operational ranges. In the early
days of Prius popularity I could tell without looking when one was
coming to a stop next to me -- and the whine recurred just as it took
off again, until the engine came on, Then, Toyota's third-gen inverters
started to come out, possibly starting with the Highlander and definitely
appearing in the hybrid Camry, which are quite a bit louder. The
third-gen Prius is equally loud because it's roughly the same
electronics. We hear it mostly due to the physical flexing of the
magnetic parts -- motor windings, boost coils, and possibly internal
wiring buses. When you're sending that much current through
something and the resultant field interacts with nearby things,
it's *going* to move.
Now switch those currents on and off at 5Khz or 10 khz and there's
your noisemaker. If the physical mounting design of the parts
accounts for these forces, you're fine over its lifetime. A Prius
actually switches modulation rate based on speeds and loads, and
varies the drive to its boost converter along with, so there's a lot
going on in there.
I hear a bit of [non-VESS!] whining at very low speeds too. I expect
it. Slight variations in how inverter parts and such get mounted and
perhaps potted, may make one Kona louder than another, and some
owners are certainly more attuned to such things.
Still, the "senior techs" at *any* maker of EVs should understand
these things. Or maybe the senior ones can't hear it anymore, and
it's up to the younger ones to appreciate the effect...
_H*