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

[Kables]

It's getting cold here in Quebec, recently over -30C.

During these cold days, I haven't driven much but I drove my 2022 Kona Ultimate and I am having an acute sound when accelerating over 50km/h (30mph). Sometimes it's WHEN accelerating over that speed and sometimes when letting go of the gas, I mean, acceleration pedal. So it kind of feels like a problem with the regenerative brakes?

What's odd is that this is intermittent. It won't do it every time I go over this speed. Sometimes it's only going to happen on the highway, so when driving over 100km/h (60mph).

It's getting less cold and the problem is still here (as of yesterday).

Here is the audio of the problem. It can be heard at 8 seconds and at 28 seconds.

 

[KiwiME]

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?

 

[Kables]

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?

1) Is your Kona parked outside in that cold?
Yes, it is parked in a tempo in the cold.

2) Does the noise disappear after about 10 minutes of driving?
Would have to pay more attention to that because I think it does disappear after some time. As I said, I don't drive much nowadays and neither far. Tomorrow I am going on a road trip so I will be able to confirm.

3) How many kms on the car?
Only 7,200km

I also posted my issue as a comment on a Reddit thread and two people confirmed they have the exact same noise when it gets really cold.

 

[Wildeyed]

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.

 

[KiwiME]

1) Is your Kona parked outside in that cold?
Yes, it is parked in a tempo in the cold.
2) Does the noise disappear after about 10 minutes of driving?
Would have to pay more attention to that because I think it does disappear after some time. As I said, I don't drive much nowadays and neither far. Tomorrow I am going on a road trip so I will be able to confirm.
3) How many kms on the car?
Only 7,200km
I also posted my issue as a comment on a Reddit thread and two people confirmed they have the exact same noise when it gets really cold.

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.

 

[Ivan Salazar]

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.

 

[Kables]

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.

Sometimes I got in my car and leave right away without preheating and the issue occurred. I will preheat the car for 10-15 minutes tomorrow before leaving and see if it occurs. It does seem like an issue with the regenerative braking because one time I put the car in neutral during the sound and it stopped right away...

 

[KiwiME]

... 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.