Low-pitch rattle, cyclical "warbling" noise

GreatJob! · **Posted:** Mon Aug 03, 2015 3:01 pm

Hi all. I am coming up on one year of CRD ownership and I have been chasing rattle after rattle since I purchased my 2005 limited with 81k miles in 8/2014 and currently have about 92,500 miles. These boards have been great for those but this one has me stumped.

The one that continues to keep coming back is a low-pitched "warbling" noise that is cyclical in nature. I have replaced the alternator (twice now) with an Advance Auto Parts unit as a way to replace the alternator decoupler pulley.

I have posted a video on youtube to show what I am talking about.
https://www.youtube.com/watch?v=zkTSTBduscg

I had the timing belt, water pump, timing belt idlers, thermostat, both engine mounts, serpentine belt, and serpentine belt tensioner replaced at 88,800 miles. I swapped the alternator out the first time around 85k miles, and at around 89k miles the noise got louder and louder until I replaced the whole alternator again (lifetime warranty). The pulley was covered in red dust, so it was a good bet. Upon replacement, the noise did get quieter, however it is back again, now as loud as ever, at around 92k miles. This time, no red dust on the pulley.

Lastly, when this is happening in the summer with the A/C on, I will also get the high-pitched rattle in the dashboard.

Any ideas? I am completely stumped. Unless the alternator decoupler on those Advance Auto Parts alternators are just that cheap, is something else going on here? My "mod" list is listed below.

flash7210 · **Posted:** Mon Aug 03, 2015 10:28 pm

Try removing the serpentine belt and then start and run the engine to see if the noises go away.

GreatJob! · **Posted:** Wed Aug 05, 2015 1:14 am

Removed the serp belt and it quieted down completely. Every other pulley or idler spun freely and quietly. The alternator decoupler is getting stiff again, however no red dust yet. Another alternator pulley 3,000 miles later? This will be my 3rd pulley in 8,000 miles. While this swap will be free under the warranty on the alternator, I am almost tempted to spend the $ on swapping the pulley out. Or is the 3rd time a charm?

Anyone else have better luck with the Advance Auto Parts units?

ebbnflow · **Posted:** Wed Aug 05, 2015 2:21 am

Your tensioner could be the culprit, causing decoupler failures. I'd replace the alternator again and then have a look at how much the tensioner dances with the engine running. A little dance is ok. A lot of dance is not.

GreatJob! · **Posted:** Wed Aug 05, 2015 8:42 am

Flow, not much dance in the tensioner at all. That was just replaced less than 4k miles ago when the timing belt was replaced with a unit sourced from Idparts.

I ordered the updated Litens 920834 pulley as suggested in another thread as I was able to get it for around $50 with coupon from Advance. Now hopefully this comes off as easily as said with a quick blast of an impact gun and 17mm hex socket.

GreatJob! · **Posted:** Thu Aug 06, 2015 8:49 am

Last night I replaced the decoupler pulley on the Advance Auto Parts alternator and put a Litens 920834 on at the recommendation of Litens via this thread: http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=78875

To my surprise, the pulley I pulled off the alternator was a #920720, also made in Canada. Same font, pattern, spacing of the text to the Litens pulley I just purchased. So, believe it or not, that cheap Advance Auto Parts alternator actually had a decent pulley on it!

The pulley I pulled off was pretty seized up. While still attached to the Alternator, I could get it to slip a little bit by spinning the armature one way and then drastically twisting the opposite way. This is very different than how the new pulley moves.

I installed the new pulley and fired it up for a test drive and sure enough, the noise is back.

I installed a new insulator that I had purchased when I bought the Dynomax exhaust as I was getting some tailgate rattle with the heavier stock system while in D or R, with my foot on the brake. I double checked the placement of the exhaust that it isn't rubbing or touching anything and it isn't.

Still, the noise is there.

To summarize what I have replaced in the last year:
Alternator (2 times and just replaced the pulley last night) 85k, 89k, 92,500.
Timing Belt, water pump, timing belt idlers, engine mounts, thermostat, fan clutch, serp tensioner, serp belt - 88,800 mi.
Mishimoto hoses, provent 200, replaced clean air hose, gde ecotune (full torque), ORM mod from 80k until GDE purchase - various mileages between 80k and current 92,500.

I've read that others have had luck by swapping trans fluid, new filter, and updated pump? Is this the next place I should look? It seems that all of the rotational items on the front of the engine are taken care of within the last 4,000 miles or so.

flash7210 · **Posted:** Thu Aug 06, 2015 10:17 am

So, you took the serpentine belt off and that made the noise go away, correct?

If thats the case, then the noise is coming from one of the pulleys.

What about with the A/C on? Does turning the A/C on cause any change in the noises?
If so, the noise may be related to the A/C clutch or pulley bearing.

Other possibilities include:
1. motor mounts. These tend to make rattly noises when bad.
2. transmission dipstick tube. If cracked or broken it will make a rattly noises.

CGman · **Posted:** Wed Aug 12, 2015 12:18 am

I'm getting ready to install #3 Advanced auto alternator in 3 years tomorrow...however my Jeep is driven about 10k-15k miles per year. It goes out every summer when the AC is used all the time. Serpentine belt squeals with AC on that gets worse as time goes on.

I'm also looking at putting the new pulley on as soon as I pick up the new alternator.

Low-pitch rattle, cyclical "warbling" noise

Who is online