So I just made a round trip drive to and from Albuquerque, NM and noticed something on the way back. I couldn't always reproduce it but if I was cruising at highway speeds and completely let off of the gas and decelerated to 60-65mph I got a loud sound coming from somewhere to the right of me that sounded like harmonic resonance. (if you've ever turned a drum or rotor without a dampener you know the sound).... if I accelerate the sound goes away. No change in drivability/mileage. I'm worried that these conditions point to the turbo having some bearing issues. Any thoughts on where to start to isolate this noise?

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Former CRD owner... now I just sit around and stare at the wall.

Have someone stand outside the vehicle and listen. Brake Torque it, and see if it makes the noise when the turbo is loaded yet you aren't moving. If you hear the noise while your not moving, look to the engine/turbo.

*Check the engine oil for excessive metal shavings.

*Pull the pipe to the turbo and check shaft play and impeller condition.

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On the other hand, if it doesn't make the noise while it is it loaded yet standing still, it might be a bearing in the drive line.

*If you suspect driveline, then jack up the rear axle and put jack stands underneath it. Chock the front wheels. Put it in drive, slowly rev it up, then down, blip the throttle. See if you can reproduce it. Once again, good idea to have someone outside of the vehicle listening too.

*Check your driveline fluids for excessive metal shavings.

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It could also be your brakes. See how modulating the brakes effects the sound when it appears. Maybe your rotors are warped or your pads are worn.

*Check the brakes for true and wear.

*Check lug nut torque (sometimes a this can tweak a brake rotor).

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Another thing to consider would be a wheel/hub bearing, although this is usually lower pitched than you are describing and is noticeable at speeds less than 30mph. Same case with the brakes.

Whatever it is, hopefully it's cheap and easy.

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--Greg
2005 CRD Sport in white
2.5" Daystar Lift Kit
245/75/16 Maxxis Buckshot Mudders

Mine has done this since I bought it with 11k on it. Specifically when cruising above 70 when I let off the go pedal the turbo seems to spool and sounds like a horn and seems like it slows the vehicle quicker. While it suprised me at 1st it is consistant and I thought it was normal, like a Jake brake effect.
Now I'm starting to get a silimar noise to a lesser degree at slower speeds. I think it might be the bearings on the turbo shaft. Makes sense that the noise is reduced at slower speeds and loud at high speeds if it is the turbo.
I have 16k left on the warranty. I need to figure out how to get the dealer to replace it. Then I may put the remote starter on the vehicle with the cool down timer to try to keep the bearing from getting damaged again.

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2006 CRD Sport Khaki

Lift Pump, Fuel Cooler
Raycor: head, filter, heater
Provent, ORM
SunCoast, TransGo, 2007 pump, B&M stacked plate tranny cooler
V6 Airbox, Wix Filter
AirLift 1000 Rear Air Bags
Fia front cover

Coming soon:
Fuel cooler bypass valve
InMotion tuning
new muffler
300,000 miles here I come