Acute sound when accelerating over 50km/h (30mph)

Ignoring for now the intermittent nature of the noise as you describe it, it sounds like the effect cold oil has on high-speed gears meshing combined with resonances in the drivetrain. The "pour point" of the oil is perhaps -45°C so the oil will be very viscous if your gear reducer was actually at -30.

1) Is your Kona parked outside in that cold?
2) Does the noise disappear after about 10 minutes of driving?
3) How many kms on the car?

A number of others have noted this noise (even myself in cool temps) and it could be considered somewhat normal. Perhaps @apu will comment?

 

Mine has developed a sound recently too. I've decided it best described as "buzzing". It's directly related to the drive train being active and has appeared very recently after 3 years and 37K km. It's annoyingly loud. Loud enough to be heard over the radio. It's been -20 degrees C here recently so am waiting to see if it goes away upon warming up.

 

Thanks for the answers. I'm quite sure I'm right about the reason but there's not much you can do about it. In any case, it's not going to be fatal but I would suggest keeping your speed down until it's warmed up, perhaps 15 minutes. You're really on the edge of the car's design envelope at that temp.

However, unrelated to this, unless it's a lease and you'll be rid of it in a few years, I would strongly suggest that you book your car in for a gear oil change at the dealer. It (probably) won't reduce the noise but will reduce the chances of gear reducer problems down the road. Don't let them talk you out of it and ask to see a sample of the old oil.

The noise is due to the collapsing of bubbles as seen in this video. In some cases particles in the oil can exasperate this condition.

 

I have been driving at -30C in Winnipeg for several days and have experience only a small noise in the first minute when stopping with regenerate brakes. Otherwise my Kona 2021 Preferred has behaved beautifully this winter with 5,000KM. The only thing I can say is that 90% of the time I’m starting with a warm battery because I charge at home and at work.

 

... because there's no regen loading the gearbox ...

If it was electronic it wouldn't change "in-tune" with car speed because the switching frequency doesn't change along with that.