I've got a 2006 CRD that all of a sudden started to do a blurring noice as I release the throttle coming into low rev positions such as intersections, or standstills.

It's kind of metallic and disappears as I rev the engine - i.e. the sound only comes up as the engine revs down and at idle it comes with an irregular pattern.

Being somewhat challenged in the mechanical field I thought it sounded as an air leak from somewhere in the exhaust - but a mechanic had a quick look and pointed at the alternator stating that the sound came from the decoupler - anyone familiar with the same phenomenon?

Sounds like U joints to me, give them a check, its a cheap & easy fix if it is.

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'04 KJ Sport SOLD 1/2017
Frankenlift II Baja + JBA Arms
4.10s, True Tracs Front & Rear
245/75/16 BFG Mud Terrain KM2's on MOABs
Renegade Lightbar
ARB Bumper + Warn M8000
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'84 CJ-7, 4.56s, Yukon Shafts, ARBs F&R, 4.5" BDS, 33x10.5r15, M8000.
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'13 Chevy Silverado 2500HD Z71 6.0L -- Stock and staying that way!

Is the sound worse in drive than in neutral, when the jeep is stopped? If so it's probably the decoupler. It's the most common source of squeaks and chirps in the CRD engine bay if it goes bad.

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05CRD: GDE Hot ECU & TCM tunes, Provent, Cat filter, Facet lift pump, TransGo kit, Florida TC, Samcos, stainless brake lines, HDS thermostat, Renegade light bar,
Bilstein adjustables, Al's Gen 4.5 Arms, 235/85-16 Duratracs, DTT rear, Elocker front, EVIC+TPMS, Turbo timer, McNally pillar gauges, Weeks Stage II kit.

Thanks for your responses.

Shows that the alternator clutch pulley didn't want to go any further. Got it replaced and that closed the case...