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Kenny Z.
Kenny Z., Ford Senior Master Tech
Category: Ford
Satisfied Customers: 5383
Experience:  Auto Trans, Drivability and Electrical Specialist
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2008 Expedition: whining in neutral

Resolved Question:

2008 Expedition makes a whining noise when you let off the accelerator and coasting. The instant you accelerate, noise stops. Louder when the engine is warm, doesnt matter if you put it in neutral while coasting. Sounds like its coming from somewhere around the back of the engine or fromt of transmission, hard to tell.
Submitted: 5 years ago.
Category: Ford
Expert:  Kenny Z. replied 5 years ago.
Hello and thanks for your question.

From your description it sounds like either a one way clutch in the transmission is starting to fail or possibly the noise is coming from the rear differential and just sounds like it if from the center of the vehicle. If it happens with the vehicle stopped then it is neither of these and more than likely coming from the engine possibly a PCV valve or vacuum leak. It is next to impossible to diagnose noises over the web, just thought I would share my thoughts based on your descriptions. More then likely the vehicle will need to be driven with a set of chassis ears microphones installed to pinpoint the noise source by a tech that has this equipment.
Customer: replied 5 years ago.

More info in case it'll help...

The sound definietly mimics the drivetrain. Sitting in the drivers seat, it sounds like its coming from the front of the console. Passenger seat, sounds like its in the dash to somewhere behind the engine(Torque converter\Flywheel area).

Seems to only do it when you have reverse thrust on the drivetrain as when you are decelerating or coasting. Almost reminds me of a u-joint thats failing except it whines and doesnt vibrate. Tranny shifting smooth, normal. It makes the sound until you are below around 10-15mph or accelerate. It does sound like an axle whine but is definietly coming from the front of the car. The pitc of the whine changes with vehicle speed.

Expert:  Kenny Z. replied 5 years ago.
Is this a 4X4? Possible front differential pinion bearing?
Customer: replied 5 years ago.
No,XXXXXLimited Edition
Expert:  Kenny Z. replied 5 years ago.
It only does it with the vehicle moving correct?

Decelerating in neutral has no affect on the noise either?
Customer: replied 5 years ago.
Correct, the whine pitch\frequency follows the speed of the drivetrain (if that makes sense). Kind of like wen you have noise on the radio from your engine.
Expert:  Kenny Z. replied 5 years ago.
It pretty much sounds like it has to be transmission if you are certain it is coming from that area. Either one way clutch or planetary gearset. Like I said very difficult on the web to try to answer noise questions. I have seen customers swear the noise is from the front when it ends up being from the rear differential. Not many noises on decell that disappear on accell other then differential.
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