I've been chasing an elusive rattle for months. It started fairly slight and has gradually gotten worse, to the point now where it is noticeable to anyone who rides in my vehicle. From reading through the forum I think it's most likely either a motor mount or the alternator decoupler. I recently noticed an occasional dimming of the headlights when the vehicle downshifted as it decelerated (coasting toward a turn or stop). The noise is sometimes there when cold and almost always there when warm. During a deceleration it is very loud right before the vehicle comes to a stop, then goes away (usually) while I set there idling with my foot on the brake (still in D). Upon acceleration it goes away (or seems to). The noise is not audible standing outside the vehicle. I can only hear it well when I am inside.

I put a long screw driver between the alternator housing and my ear but can't discern any noise there aside from the engine. I did the same at the bottom of the vehicle (where the noise was slightly audible over the engine noise) by placing the screw driver against the cross member in front of the oil filter. Here I can definitely hear a banging (very metal on metal sounding) that's not part of the normal engine noise. I also tried putting the screw driver against the exhaust, but only normal engine sounds there.

It seems like a motor mount to me, but I'm not sure what to look for or how to diagnose it for sure. Laying under the vehicle to watch the motion of the mounts while someone puts it in drive seems dangerous, and I'm not sure how much motion I should see.

Has anyone had an issue like this? What should I look for to indicate a failed mount? If I remove the belt to check the decoupler, what would evidence a failure with that (free spinning, gritty feeling, not turning)? I haven't noticed any chirping or squealing.

Anything else I should be looking at? I'm doing my transmission and transfer case service this weekend...should be a Jeep-a-rific weekend.

Thanks in advance for any suggestions or insight.

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2006 CRD Limited
SEGR Mod
Saikou Michi Condenser -- Deleted
Samco Hose Kit
Fumoto 102
Etecno1 GX3123 Steel 7V Glow Plugs
GDE FT Eco and Hot Tunes
JBA 4.5 UCAs
OME Lift

Mine has done this since it was new.

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2005 sport crd-SOLD No regrets

Take the serpentine belt off and have a quick listen for the rattle. If the rattle noise goes away, then it is most likely your alternator decoupler or an idler pulley. Often when the decoupler is worn out, or locked up, then the noise will come from the belt tensioner (excessive movement). So....pop the belt off and have a quick listen. Keep an eye on the temp gauge while running with the belt off.

Hope this helps,


Javert

In the past there has been instances where people have found loose bolts on the right, passanger side, motor mount But this will have nothing to do with lights dimming.

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Atlantic Blue 06 CRD Limited (his)
Joined by a 2000 XJ Classic (hers)

My passenger side motor mount was loose about 5 turns of the nut solved that problem 3 years ago and just last august my alternator decoupler / pulley broke I replaced it with the new part # 53013554 AE alt pulley much shorter on the front end plus I took all the other pulleys off and cleaned them and put some high temp grease on the inside of each one and I have had no problems or squeaks since then. I do from time to time put a little dielectric grease on the grooved side of my serpentine belt to keep it running very quiet. I check my tensioner pulley once a week and it does not move at all I think the grease on the inside of the pulleys helps a lot. I am at 98,000 now and just a few problems with the crd over the years.

Well, I tried the top and bottom nuts on the motor mount today and couldn't turn either of them.

_________________
2006 CRD Limited
SEGR Mod
Saikou Michi Condenser -- Deleted
Samco Hose Kit
Fumoto 102
Etecno1 GX3123 Steel 7V Glow Plugs
GDE FT Eco and Hot Tunes
JBA 4.5 UCAs
OME Lift

When my motor mount was loose it made a very slight click sound when I came to a stop and then when I would take off from a dead stop. The other weird problem that I had was a rumbling vibration when I would slow down from high speed on the highway kind of like driving over rumble strips on the side of the highway. That problem turned out to be the rear u joint. The joint was completely dry so I had my mechanic put in a joint with a Zerk fitting so I could grease it a little every oil change. The joint cost about $60 less than the jeep non greasable joint go figure.