Persistent High Frequency Whine in Cabin

[catrikejoe]

I thought about that, but I think unpowering the EBB alone may cause the car to throw a bunch of errors. Don't want to risk that. I will certainly point the tech towards a process of elimination scheme like that though once it is at the shop though.

If you had Forscan you could always erase those trouble codes.

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[BeaverRat]

If you had Forscan you could always erase those trouble codes.

True, I should probably do that. I would also turn off auto start-stop then.

I see you have a 2025 BS BL (this should have the same EBB as my 2026), if you pop your hood, do you hear the same high pitched sound after unlocking/waking up the vehicle?

 

[DWG]

The dealer used Chassis ears to pinpoint the brake pedal clicking noise I was getting to the Brake Power Booster. Since you were able to pick up the noise with your phone do you think the technician would be able to confirm the noise through the chassis ears?

 

[BeaverRat]

The dealer used Chassis ears to pinpoint the brake pedal clicking noise I was getting to the Brake Power Booster. Since you were able to pick up the noise with your phone do you think the technician would be able to confirm the noise through the chassis ears?

Perhaps. Depends entirely on the frequency response of this ChassisEars device. Their spec sheet was very sparse on key specifications I would be interested in understanding for an audio based device. If it does indeed pickup and amplify the 13.8 kHz noise though, then they should be able to use it, with the huge caveat that the operator also has to be able to hear this frequency with his own ears. It does not appear to be a frequency spectrum measuring device (that represents what it measures on a visual display), but rather a set of wireless microphones you spread around the vehicle to pinpoint abnormal noises.

 

[DWG]

I understand. Thank you.

 

[catrikejoe]

True, I should probably do that. I would also turn off auto start-stop then.

I see you have a 2025 BS BL (this should have the same EBB as my 2026), if you pop your hood, do you hear the same high pitched sound after unlocking/waking up the vehicle?

NO so far it's quiet, I'm always listening for different noises being a mechanic.

 

[Arcee]

I have a 2025 Big Bend. I hear a similar high pitch tone in the engine bay of mine after unlocking. I do not hear it from inside the vehicle, however.

 

[NMBroncoSport]

This is from AI:

My current ranking would be:

1. BCM or another body electronics module coil whine — 40%
2. ADAS/camera/radar electronics — 25%
3. Telematics module — 20%
4. Other DC-DC converter/regulator — 15%

The most likely suspects:

1. Body Control Module (BCM) / Gateway module power electronics — my top suspect

The BCM is one of the first things that wakes when you unlock the vehicle. It controls or coordinates:

* lighting
* locks
* alarm
* interior electronics
* network communications
* wake/sleep states of other modules

The BCM itself may not be the sound source; rather, a voltage regulator, inductor, or DC-DC converter inside or near it could be vibrating at its switching frequency.

A 13.8 kHz tone is very plausible for this.

2. ADAS / camera / radar modules

The Bronco Sport has several driver-assistance systems. Modules that wake immediately include:

* front camera system
* radar-related electronics (if equipped)
* parking sensors

These contain switching regulators and processors that can generate audible coil whine.

A clue would be whether the noise location is near:

* windshield/cowl area (camera electronics)
* front grille area (radar/sensors)

3. Telematics Control Unit (TCU) / modem

The vehicle’s cellular modem wakes when the car wakes. The TCU contains:

* processor
* cellular radio
* power regulation circuitry

Some owners of newer vehicles have reported audible high-frequency electronic noises from telematics modules.

4. Instrument panel / infotainment-related power supply (not the display itself)

You ruled out the screen, which is good. However, the power supply feeding the display system could still be responsible.

Many automotive electronics have:

* buck converters
* inductors
* switching regulators

The display can be quiet while its power electronics whistle elsewhere.

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A useful diagnostic approach

Given your methodical elimination, I would next do module isolation, not component guessing.

With the noise present:

1. Open the hood.
2. Use a mechanic’s stethoscope (or even a length of hose as a listening probe).
3. Compare:
* fuse box area
* firewall/cowl area
* battery area
* front grille area
* left/right fender areas

You are listening for the physical vibration of the component, not the airborne sound.

A second very useful test:

Pull fuses one at a time (with a memory-safe approach)

If you can identify candidate circuits:

* Body control
* Telematics
* Camera/ADAS
* Infotainment

Pulling the fuse that kills the tone identifies the system. (On a new vehicle, I would be cautious and document everything.)

 

[BeaverRat]

Brought it in to the dealer. They confirmed that the noise was indeed coming from the electric brake booster. The debug was difficult, as most of the service advisors and technicians could not hear it. Only one of the young guys was able to really hear it as well as me.

The bad news, they didn't have a like-for-like model on the lot, so they were unwilling to appreciate that the same exact brake booster in a slightly different model was noticeably quieter. No swaps on the booster can be performed unless mine is deemed significantly more noisy than one in an identical model.

For next steps, they're going to get in touch with their Ford FAE, and discuss options. I'm also hoping they'll get a badlands in stock at some point...

 

[DWG]

Brought it in to the dealer. They confirmed that the noise was indeed coming from the electric brake booster. The debug was difficult, as most of the service advisors and technicians could not hear it. Only one of the young guys was able to really hear it as well as me.

The bad news, they didn't have a like-for-like model on the lot, so they were unwilling to appreciate that the same exact brake booster in a slightly different model was noticeably quieter. No swaps on the booster can be performed unless mine is deemed significantly more noisy than one in an identical model.

For next steps, they're going to get in touch with their Ford FAE, and discuss options. I'm also hoping they'll get a badlands in stock at some point...

This is an issue I have encountered as well. The dealer tends to have mostly lower trim models on the lot ao they have nothing to compare a noise to so even though they hear it the will not do anything. What is even worse is they have the same model and year on the lot and it makes the same noise so they chalk it up to normal and when they reach out to Ford the engineers just says you compared the noise to a similar model and it was the same. Nothing to repair.

When my BS was new I noticed a grinding noise at low speeds from what sounded like was coming from under the engine especially when making a right turn from a stop like at an intersection. I drove with the Forman who verified the noise. Per Forman not RDU. Since another BS made the same noise I have to live with it. Just because another same model makes a specific noise doesn't mean it is a normal noise that I should be hearing. It just means bad engineering or bad quality control that I have to live with.

I hope you are able to get a satisfactory resolution to the brake booster issue. I know how annoying these noises can be and just because they can duplicate the noise in another same model doesn't make the noise normal.

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