Buzzing from rear of car after new RDU installed - dealer doesn’t know why

[brandim]

A month ago I had a brand new RDU installed after I was having a grinding when turning sharp. After that repair, I started hearing a loud buzzing noise from the rear of my car anytime I’m above 35mph. It’s a constant noise regardless of acceleration, turning, etc. I took it back and they claimed it was a bent heat shield, but it still made the noise. Took it back a second time and they continue to claim it’s not an RDU issue even though that’s when I started hearing the noise. I found on Reddit the idea to turn off traction control and when I do that, th noise immediately stops like flipping a switch. The dealer looked at it again and now they’re saying it could be a brake issue, but they’ll start charging me to look into it further. My car has about 59k miles on it. Anyone had this same issue and figured out the problem? I’m fine turning off the traction control to avoid the noise but if there’s a serious issue I don’t want to keep driving on it and making it worse.

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[Chiefthepup]

Per chat gpt so take it with a grain of salt


On a Bronco Sport, a buzzing or humming from the rear that stops when you turn traction control off is almost always normal operation of the traction/ABS system, not a failing differential.





Here’s what’s going on














What’s actually making the noise








Your Bronco Sport uses brake-based traction control + an electronically controlled rear drive unit (RDU).





When traction control is ON, the system:

• Pulses the rear brakes to stop wheel slip
• Engages/disengages the rear clutch pack
• Uses the ABS pump to modulate pressure

That pulsing creates a:

• Buzzing
• Grinding
• Electric “whirr” or vibration

When you turn traction control OFF, those brake pulses stop → noise disappears.














When it happens most








This is especially common during:

• Slow turns in parking lots
• Tight U-turns
• Wet pavement
• Gravel or uneven surfaces
• Light throttle while turning

Ford’s AWD tuning is very aggressive, so the system intervenes early.














This is considered NORMAL if:








No warning lights


No clunks or bangs


Noise only happens while moving/turning


Noise stops when traction control is off





Many Bronco Sport owners report the exact same thing.














When it might NOT be normal








Get it checked if you notice:

• Loud metal clunks
• Noise even while driving straight
• Vibration at highway speed
• Burning smell
• AWD / ABS warning lights

Those could point to:

• Rear drive unit fluid issue
• Wheel bearing
• Faulty ABS sensor

What you can do

• Leave it alone if it’s mild (most do)
• Turn TC off temporarily in parking lots
• At next service, ask them to:
  • Check rear drive unit fluid
  • Check for ABS/traction control updates

Bottom line








Nothing is “breaking.”


You’re hearing the traction control system actively working — and turning it off proves that’s the source.

 

[Ernest T]

A noise that wasn’t there before a part was changed is a giant red flag. Stopping when you turn something off. Is another. I’d hound my dealer and/or elevate the issue to Ford.

 

[Whpony96]

I can tell you this our 2025 Bronco Sport Badlands doe not make that sound. Nor has it ever. It's 100% NOT Normal! It didn't make it before then it's NOT RIGHT. Not all techs are created equal. I'll bet that was the techs first RDU and when he tore it apart he did a "opsie". Understand you can go to any Ford service authorized shop. They do not have to be a Ford dealership. One of the best out there is Brian @ FordTechMakuloco people send him their vehicles from all over the nation to get worked in. https://www.youtube.com/user/FordTechMakuloco That said I would highly recommend going to a new shop to have it looked at.

 

[fjbear!]

A month ago I had a brand new RDU installed after I was having a grinding when turning sharp. After that repair, I started hearing a loud buzzing noise from the rear of my car anytime I’m above 35mph. It’s a constant noise regardless of acceleration, turning, etc. I took it back and they claimed it was a bent heat shield, but it still made the noise. Took it back a second time and they continue to claim it’s not an RDU issue even though that’s when I started hearing the noise. I found on Reddit the idea to turn off traction control and when I do that, th noise immediately stops like flipping a switch. The dealer looked at it again and now they’re saying it could be a brake issue, but they’ll start charging me to look into it further. My car has about 59k miles on it. Anyone had this same issue and figured out the problem? I’m fine turning off the traction control to avoid the noise but if there’s a serious issue I don’t want to keep driving on it and making it worse.

Go to a better dealer before warranty is up. They put a used one in i bet

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