im also experanceing a squreal and rattle under the hood and i have no idea what it is.

It's the pulley ON the alternator - the decoupler is inside the part that the belt spins on. I believe the part is 53013554AF, just under $70 before shipping at mmaautoparts.com (for example).

You'll need a special tool (most likely) to remove and replace it. You can buy the decoupler separately to avoid having to purchase the combined alternator/decoupler ($$$). If you have an pneumatic wrench it may break loose without the tool.. but guarantees.

The tool is Miller Special tool, p/n 8433.

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2005 Liberty CRD
2004.5 Cummins 5.9L TD, F1s, NV5600 6-speed in a '93 GMC Suburban

Hello and welcome to the forum. You should take a look at the noob guide here:
viewtopic.php?f=5&t=54207

The first image will familiarize yourself with the engine bay....including where the decoupler pulley is.

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http://www.Colorado4Wheel.com
"Its not about what you can DO with your Jeep, its about where you can GO with your Jeep."
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BTW - most likely, the squeal/rattle *is* due to the decoupler. Rattle is the thing itself, squeal is the belt protesting.

It's hard on the tensioner (bottom/left as you face the engine from the front) because of all the jerking, so check the idlers to see that their bearings are healthy when you change the part. If the idler spins freely for seconds when you flip it, that probably means the bearing grease has left the scene - sound idlers spin smoothly but stop fairly quickly (when cold, at least) because of the internal lubricant's friction. Of course, any gritty/jerky feel or sound means the bearing's shot and the idler is best replaced. $20 at NAPA, $70-$80 from the stealer.

It's also hard on the belt, so you might as well replace it too.

Mark

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2005 Liberty CRD
2004.5 Cummins 5.9L TD, F1s, NV5600 6-speed in a '93 GMC Suburban