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An uncertain noise...


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Alright, so as the weather continues to get warmer, I find myself with the window down more and more. As nit picky as I'am I seem to get myself well-attuned to things when I use it or operate it enough.Well, as it may have it, my eagle ears picked up a paculiar noise. Performance wise, I do not seem to notice a difference. So my curiousity arouses me...Driving home at the 30mph limit, I noticed a sort of rattling. I can definitely hear it better when at a light stopped. So when I pulled up to my house and parked it, the noise went away. Put it back into gear, and the rattle noise came back. Put it into Park, and the noise goes away...ANYONE have any idea what it is?I was trying to think about what it could be and I remember something about a ratlle sort of noise from something called the TV cable?Could that be it?

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Mine is a super loud rattle at 1400 rpm any gear. I think its a cracked flex-plate.

... or maybe your driving a Cummins Diesel! :lmao::lmao2: Seriously... Most noises you can isolate by seeing if it changes by acceleration, coasting, putting the transmission in neutral, etc. So if the noise changes it might give a clue to its location.
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Sometimes the only way to find noises which aren't easily identified is with the help of a mechanic stethoscope. Looks just like a doctors stethoscope but with a stick like pointer end instead of what you'd normally see on a stethoscope. I've never had to buy one because a cheap piece of wood (like a dowl rod or thin broom stick) works just as perfect. Length would be personal preference too. Simply hold one end of the stick with your fist covering the end, placing your fist up to your ear, and touch the other end of the rod to any part of the truck, engine, or transmission, etc..... You'll be amazed how noises only pertinent to whatever you touch will travel through the rod/stick. It works so well that you can even single out noises of components under the hood while the noisy Cummins is running. Just be careful around moving parts.

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  • 2 weeks later...

Okay, so, its been a little since I've been able to take some time and try and isolate this pesky noise. It was very pronounced today after getting on the skinny pedal for a little. It seems like its a noise thats amplified through harmonic vibration.It ended up continuing to produce this noise even after I put it into park. So I had a chance to jump out and try and track the noise down. Right off the bat, it was coming from under the truck. So, I took a walk-around and I believe I narrowed it down.My suspicion all along was that it was something to do with the exhaust. I was on the passenger side and I crouched down and put my boot on the exhaust, instantly, the noise went away. Took my boot off and it came back.Got under the truck when it was shut down and banged it with my fist. There is some sort of debris in the exhaust or some sort of inadvertent contact going on with the pipe that is causing the noise. The noise is most pronounced right before the U-bend going over the rear-end.I cannot think of how anything could be in there except for exhaust fins from the turbo. Either that, or when my exhaust guy was putting on the new run of pipe, his welding wire finally broke off on the inside.I don't believe I have ever pushed the truck hard and recently to cause a failure of the turbo of some sort.I sure wish I had a camera to stick down the pipe!

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They make them. If you know a plumber they might have one. I have had to tv more than one sewer line.

Oh, I know they make 'em! :wink: Its just I dun have a plumber as a friend or know anyone who has one, nor have the cash to get one, lol. I might try the ol' mcgyver thing. See if I can fish a magnet down the exhaust on some stiff something.
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I have never touched the exhaust, so I dunno. When I bought the truck, the exhaust was straight piped. Where I assume the muffler and cat converter were, they put in 4" flextube. It was rusting out, so I had my exhaust guy put a 3" straight pipe. It is all now 3" straight piped from the turbo back. Its got a 5" miter cut exhaust tip.

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Being straight piped, there really isnt anything to go bad unless there's holes or cracks or unless maybe there's something up with one of the hangers where maybe the rubber is shot. Since you've narrowed it down, with the engine off, you might just want to try getting under the truck and tapping on the exhaust with a light hammer from the front to the rear, listening for any strange rattles or odd sounds.

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Alright, so I figured out why the rattling noise is occuring. Upon inspection with a mallet and a mirror, I checked the exhaust pipe over.The U-bend over the rear-end is rusting out. I would have never seen it if I did not use a mirror..My theory is the pipe is rusting out to the point a bunch of the rust is collecting and making the notorious rattling noise.So, I could either fix the area thats rusting, and keep patching the exhaust like this until its all replaced, or I could go with a new exhaust system.I wonder if a 4" exhaust would be of any benefit for me? Called my exhaust guy and he said the pipe would have to be special order as no one in our area can bend 4" pipe.He quoted me $450 with a 4" kit installed by him. Should I go with it or order online and DIY it? Or should I stick with a 3" system and get it all replaced or just fix the spot thats rusting?

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I'll be interested in hearing this one out on exhaust size. Six years ago I was convinced that the 4" was the way to go. But after seeing Mikes success with a 3" straight pipe and some others with the same set up, I am not as convinced the 4" is that beneficial. With what I have plus maybe 50 more hp, is a 4" exhaust necasary?

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I'll be interested in hearing this one out on exhaust size. Six years ago I was convinced that the 4" was the way to go. But after seeing Mikes success with a 3" straight pipe and some others with the same set up, I am not as convinced the 4" is that beneficial. With what I have plus maybe 50 more hp, is a 4" exhaust necasary?

I was looking at 4" because it seems like it helps with keeping low EGT's?
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That was my thought process 6 years ago, but after seeing Mike succes and some others it make me wonder. Mike's 3" seems to be keeping up with his mods and EGT's quite well. Not that mine does not, thats what makes me wonder.

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My OEM 3" straight piped "seems" to be working just fine too but in saying that I have nothing to compare with and really the factory 3" isnt really a "true" 3" system either since its not mandrel bent which means in reality its probably more like 2.5". And the reason I chose to remove the muffler and resonator was to keep the EGT's as low as I possibly could given the trailer weight I occasionally tow. The EGT's stay reasonable but the noise has become unbearable. Its just to freaking loud and becomes obviously annoying to others as I try to quietly sneak in/out of RV parks, or while wait for my kids to get out of school on hot days, etc..... So my plans are to get a 4" system with a muffler so that I can maintain the EGT reduction but reduce the noise as well. And maybe I'll experience a little performance gain too but reducing the noise will be worth the cost.

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Generally up to about 350 to 400 hp the stock exhaust is just fine. Over 400 hp you would want a 4" system. From what I understand there would be no one on here making enough power to require a 5" system. Even semis have 4" and they make a fair bit more power than we do. If you go to big you can cause the EGTs to climb!! The reason for that is because the exhaust never gets warm and since cooler air is more dense it takes more effort to push it out.

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