NX 450h+ hum at standstill?

AlanDL · October 31, 2022

I have had the car for 3 weeks now, and have noticed a high pitched hum when not moving. It's not loud, but it is quiet and noticeable (and my hearing isn't that good at high pitched noises!). As soon as I move off the hum goes. It is clearly an electrical sound, as the car is in EV mode. Happens regardless of the level of charge left in the Battery.

I thought it might be due to it being brand new, something not quite run in yet, like a flywheel or something. I don't recall hearing this on the test drive (which was many months ago). Has anyone have any experience of this or suggestions or what it might be please?

If not, I will contact the dealer to have a look (I am going on a long run at the end of the week so it will have a few hundred miles on the clock then).

ColinBarber · October 31, 2022

Does it do it when in Neutral?

AlanDL · October 31, 2022

Thanks I will check on that. It doesn't do it when I first start the car, but I think it does start when I move it. I will test it out when I go out next.

royoftherovers · October 31, 2022

2 hours ago, AlanDL said:

Thanks I will check on that. It doesn't do it when I first start the car, but I think it does start when I move it. I will test it out when I go out next.

So, the car is not in EV mode at start Alan ?

Harrier Man · October 31, 2022

I cannot say that I have noticed a high pitched hum on my 450h+ but I guess this is subjective as I do hear some noises. These seem more noticeable as the colder weather has approached but, again, that is subjective.

P33 of the manual describes various noises that might be heard. I do notice the main Battery cooling fan operating but I wouldn't describe it as a high pitched hum or even noisy.

AlanDL · October 31, 2022

1 hour ago, royoftherovers said:

So, the car is not in EV mode at start Alan ?

It is in EV mode at the start, but I think I don't notice the hum until the wheels are turning, so engaged in Drive or Reverse. I will take more notice of what happens at standstill, and what happens if I put it into Neutral if it is making the hum when at standstill.

NemesisUK · October 31, 2022

Could it be the climate control? The fans don't start up immediately on starting the car.

Being in EV mode could it be some form of cabin and/or Battery pre-heater?

AlanDL · October 31, 2022

18 minutes ago, Harrier Man said:

I cannot say that I have noticed a high pitched hum on my 450h+ but I guess this is subjective as I do hear some noises. These seem more noticeable as the colder weather has approached but, again, that is subjective.

P33 of the manual describes various noises that might be heard. I do notice the main battery cooling fan operating but I wouldn't describe it as a high pitched hum or even noisy.

Thanks: and thanks for saying that the "Traction Battery cooler" is a fan, as that would make sense: as I notice the noise at very low speed, that would most likely be when a fan is operating. Also on start up, the fan might not be on if the car is not moving. I will have a chance tomorrow to check how all that fits in. It is that, then is this a factor with full EVs, which obviously have much bigger batteries and more heat. Or is it that I have a noisy fan! I will gather more information.

AlanDL · October 31, 2022

Just now, NemesisUK said:

Could it be the climate control? The fans don't start up immediately on starting the car.

Being in EV mode could it be some form of cabin and/or battery pre-heater?

I have not been using the AC: unlike the previous NX, this one seems to default to having the AC off on at start-up: probably good, as at the moment the weather not extreme hot or cold.

NemesisUK · October 31, 2022

7 minutes ago, AlanDL said:

I have not been using the AC: unlike the previous NX, this one seems to default to having the AC off on at start-up: probably good, as at the moment the weather not extreme hot or cold.

I would highly recommend leaving the a/c ON this will condition the cabin air, removing dampness in the cooler months and prevent the windows steaming up. Additionally leaving the a/c ON helps lubricate the system seals, preventing them drying out and leaks developing.

The climate control system really does operate far more efficiently and effectively if the a/c is on and the system set to automatic, just set the temperature you find comfortable and let the car do what it's designed to do.

royoftherovers · October 31, 2022

8 minutes ago, NemesisUK said:

I would highly recommend leaving the a/c ON this will condition the cabin air, removing dampness in the cooler months and prevent the windows steaming up. Additionally leaving the a/c ON helps lubricate the system seals, preventing them drying out and leaks developing.

The climate control system really does operate far more efficiently and effectively if the a/c is on and the system set to automatic, just set the temperature you find comfortable and let the car do what it's designed to do.

I agree. Leave the AC on ALL of the time as Peter recommends.

Ken R · October 31, 2022

I can't say that I have heard any unusual noises. Are you not just hearing the statutory warning noise for EV's when travelling (forward and reverse) at low speed? That of course wouldn't account for the noise when stationary.

AlanDL · October 31, 2022

42 minutes ago, Ken R said:

I can't say that I have heard any unusual noises. Are you not just hearing the statutory warning noise for EV's when travelling (forward and reverse) at low speed? That of course wouldn't account for the noise when stationary.

No, I had not given that a thought! Nobody at the dealership mentioned that, and I cannot find any reference to AVAS in the manual: but clearly it does apply to plug-in hybrids as well. Presumably Brexit would not have affected the regulations here. That would fit in well with what might be happening: again, I will check it out when driving tomorrow. I am not sure it makes any noise when actually at standstill. I will have the windows open as well (raining hard here at the moment). Thanks for your suggestion!

Hillie · October 31, 2022

This is a long shot and I do not know if you have an F-Sport Model, but the F-Sport models have an "Active Sound Control" feature that attempts to make a more sporty engine noise in the cabin. At standstill could this speaker be causing the hum inside the vehicle? The specs suggest there is a volume control for this and I confess I have no idea where it is.

Caspa · November 2, 2022

On 10/31/2022 at 4:55 PM, AlanDL said:

No, I had not given that a thought! Nobody at the dealership mentioned that, and I cannot find any reference to AVAS in the manual: but clearly it does apply to plug-in hybrids as well. Presumably Brexit would not have affected the regulations here. That would fit in well with what might be happening: again, I will check it out when driving tomorrow. I am not sure it makes any noise when actually at standstill. I will have the windows open as well (raining hard here at the moment). Thanks for your suggestion!

It's certainly this as didn't read the title, and it was the first thing that came to mind when reading your description of the sound. Most noticeable when pulling away I find.

AlanDL · November 3, 2022

10 hours ago, Caspa said:

It's certainly this as didn't read the title, and it was the first thing that came to mind when reading your description of the sound. Most noticeable when pulling away I find.

AlanDL · November 3, 2022

Just now, AlanDL said:

I think this is it!

AlanDL · November 3, 2022

I had a chance on a quiet carpark to test the whole issue. The sound only occurs when the wheels are moving, whether it is in Drive or Neutral. No sound when at standstill, despite my topic header (sorry about that, must have had persistence of hearing or something). What Ken R said and Caspa just reinforced seems to be the most likely explanation. In addition, I noticed that the sound disappeared at 14mph, whether the car was accelerating or slowing down: 14mph was the critical point. Looking at the AVAS regulations, in the US the sound has to be audible at 30kph, but in Europe it is 20kph, ie approx 14mph. So that looks like proof to me. The noise is still a low level single note buzz: it is difficult to hear the outside noise with the windows down, but I was more sensitive to some additional inside noise that sounded like a normal car engine pulling away. I am not sure whether the hum/buzz noise is a particular frequency of the noise outside, or just a notification of it, or part of the mechanism to activate the outside sound: but it is clearly associated with the AVAS. Thanks to everyone for helping me with this: noise is not annoying as long as one knows there is a reason.

royoftherovers · November 3, 2022

25 minutes ago, AlanDL said:

I had a chance on a quiet carpark to test the whole issue. The sound only occurs when the wheels are moving, whether it is in Drive or Neutral. No sound when at standstill, despite my topic header (sorry about that, must have had persistence of hearing or something). What Ken R said and Caspa just reinforced seems to be the most likely explanation. In addition, I noticed that the sound disappeared at 14mph, whether the car was accelerating or slowing down: 14mph was the critical point. Looking at the AVAS regulations, in the US the sound has to be audible at 30kph, but in Europe it is 20kph, ie approx 14mph. So that looks like proof to me. The noise is still a low level single note buzz: it is difficult to hear the outside noise with the windows down, but I was more sensitive to some additional inside noise that sounded like a normal car engine pulling away. I am not sure whether the hum/buzz noise is a particular frequency of the noise outside, or just a notification of it, or part of the mechanism to activate the outside sound: but it is clearly associated with the AVAS. Thanks to everyone for helping me with this: noise is not annoying as long as one knows there is a reason.

I found this quite informative Alan https://mag.lexus.co.uk/lexus-and-the-art-of-noise/