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Old 10-08-2009, 10:07 PM   #1
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Really Friggen' Irritating rattle

94 2.5 5 speed, soft top...between about 1600 and 2300 RPM's, regardless of what gear I'm in, there's a friggen annoying rattling-sounds like it's coming from somewhere behind the passenger seat. I looked under, thinking it was a heat shield...didn't really find one loose enough to rattle like that. What I DID find, was that my Catalytic Converter is pretty much touching the transmission skid plate, so my guess is that is my pain in the ass rattle, and those rpms just happen to be violent enough to rattle it. It's pretty much the only thing wrong with my jeep at the moment...and it's got to go. Any ideas on how to stop this rattling, or any suggestions as to what it might be other than that?
Thanks in advance.

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Old 10-08-2009, 10:12 PM   #2
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When my cat was doing this, it was due to the cat's ceramic core breaking up.
Chunks of it would rattle around in there like popcorn, then shoot out the tailpipe after a while. Some would be big enough to partially block the exhaust flow & cause power loss.

I took that cat out & was gonna replace it, honestly I was.

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Old 10-08-2009, 10:18 PM   #3
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Hahaha. Well, that's the thing though..It doesn't seem like that. It's all the time...when it first starts, idle, accelerating, any time it's in those rpms...hit about 2350 and it goes away. Drop back down, and it comes back. There is no rattle at any other RPM...but it's literally touching the skid plate.
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Old 10-08-2009, 10:23 PM   #4
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Hahaha. Well, that's the thing though..It doesn't seem like that. It's all the time...when it first starts, idle, accelerating, any time it's in those rpms...hit about 2350 and it goes away. Drop back down, and it comes back. There is no rattle at any other RPM...but it's literally touching the skid plate.
I can't remember if mine had rpm related differences. Might be that at higher rpms the loose chunks get pinned wherever they are.

I wonder if you motor mounts are sagging enough to let the cat touch the skidplate. I wouldn't suggest trying to pry the cat up off the skid though, it might crack the cat connections. Maybe you could use an exhaust hanger to move it enough to clear.
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Old 10-08-2009, 10:28 PM   #5
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Ahh...that wouldn't be fun. The motormounts aren't in the greatest of shape, but they are still pretty solid. I'd give pictures and stuff...but a digital camera is something I don't have. and that could be...and maybe at lower rpms it's not strong enough to move them at all. I'll get under there and try to see if I can get a vibration into it and see if it rattles chunks..if it does, screw it, it's $76 for a magnaflow on quadratec.
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Old 10-08-2009, 10:36 PM   #6
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Look at the ground behind the jeep where you normally park & warm it up each day.

The core chunks would blow out the tail pipe & they are like off white of tan colored & have little square tubes running through them. Maybe an inch long sometimes. They crumble easily because they are ceramic.

The cause of this may be if the engine is not running properly for emissions. The core gets too hot & starts to melt in some spots. As they cool, these hot spots take longer to cool & crack the surrounding areas allowing pieces to break off.
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Old 10-08-2009, 10:39 PM   #7
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Well, I've never really noticed that anywhere. The other day I held it at around 2000 for a few minutes in neutral to heat up the engine cuz it was friggen cold, didn't hear anything hit the car behind, no one complained, and I've never seen those chunks anywhere...but I will look. I'm still thinking it's just touching that though- I was wondering if there was anything I could put between the cat and the plate...but I can't think of anything thin and with a dampening effect that doesn't melt or burst into flame at 500 degrees.
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Old 10-08-2009, 10:42 PM   #8
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Do you have a spool of wire? Tie it up using your frame and and see if it stops.
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Old 10-08-2009, 10:44 PM   #9
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You don't happen to have the jack in the under the passenger seat location still, do you?

Might want to remove and do a quick spin if you do.
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Old 10-08-2009, 10:47 PM   #10
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no...jack is still in the standard place, which for this jeep is under the hood.
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Old 10-08-2009, 10:48 PM   #11
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Do you have a spool of wire? Tie it up using your frame and and see if it stops.
I do, as a matter of fact. I'll go grab that now and put it in my kitchen so I remember tomorrow..it's almost midnight here.

I feel quite daft now actually..I can't believe I didn't think of the wire idea >.>
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Old 10-09-2009, 06:42 PM   #12
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I do, as a matter of fact. I'll go grab that now and put it in my kitchen so I remember tomorrow..it's almost midnight here.

I feel quite daft now actually..I can't believe I didn't think of the wire idea >.>
My exhaust has a stainless wire holding it up, that used to be a radio antenna. It was a be-och to twist it with two large pairs of vise grips, but it's been holding up nicely.

A coat hanger will work for the test, but it'll rust away in no time.

Also those core bits will be fairly small, smaller than an AAA battery, by the time they make their way through your muffler.
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Old 10-09-2009, 08:44 PM   #13
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Although I have a 4.2L motor, I too had a rattle that was beyond the pale! Motor mounts solved problem 100%. Mounts and the rubber isolaters look O.K. but after changing gave me a quiet ride.

Good luck, Fred
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Old 10-09-2009, 09:37 PM   #14
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I noticed the same noise a couple days ago. I am new to having a manual vehicle as a dd. I noticed it when I was starting out from a stop. I thought it was the clutch. The rpm's must be just right to cause the violent exhaust rattle when i'm starting to roll and it hits my transmission/ transfer case skid plate. Then I noticed that the exhaust hanger that slides into the transmission torque arm plate was broken off. So I guess i'll have to rig it up with a coat hanger until I replace then exhaust or atleast the front pipe.
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Old 10-10-2009, 01:10 PM   #15
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I use to get a real loud obnoxious sound from some where near my passenger seat. It quit, once I left tha Ole Lady at home. ( I know, but I couldn't help myself)
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Old 10-10-2009, 10:53 PM   #16
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I use to get a real loud obnoxious sound from some where near my passenger seat. It quit, once I left tha Ole Lady at home. ( I know, but I couldn't help myself)

Mine still makes those kind of noises. I hate this friggin jeep, it always messes up my hair!!!

Took her out to dinner tonight in fact, had to take the minivan.


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Old 10-11-2009, 03:48 PM   #17
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Finding the right Co Pilot, to ride around in an open jeep, is like finding a good one to ride on tha back of a Bike. If they ain't in to it, ya might as well leave it in the garage. They will make ya wish ya never left tha house. And you all know just what I'm talkin about.
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Old 10-11-2009, 04:50 PM   #18
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I stuck some flat washers under it...and the rattle stopped. It's not core pieces...the metal casing on the outside is pretty much rotted away and loose. To make matters worse, today the rattle essentially stopped mostly...so something tells me when I go under there there will be a little less cat there then there used to be.

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