New Mod, New Rattle

TenThumbs

TenThumbs

New Member
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Jun 1, 2018
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24
Location
Cypress, Texas
Hello all. New here. Need some help with a rattle. I installed a MBRP Cat Back exhaust to the stock cat on my 04 TJ. The rattle occurs only when accelerating in drive and stops as soon as I let off of the gas. At first I thought it was the fan hitting the fan shroud but have ruled this out by installing a 1' BL and MML. The install of the exhaust was a tight fit. I have checked all of the hangers and pipe. Everything is free and clear of hitting something else. Could this be a bad cat or something else? Any help would be much appreciated. I've spent hours looking for the issue and am stumped.

Edit: Thought I'd list more info for the peekers in the hopes someone will have an idea. If I put the Jeep in drive and lightly give her gas, not rattle/knocking. As I pick up speed, the rattle knock starts and the faster I go, the faster the noise.
 
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I think not related, but I don't want to lead you into my line of thinking, I am no where near an expert of cat. A while back, many moons ago I had a 3500 utility van and your symptoms lead to a bad cat. And then I read somewhere on this forum about the same fix on the same symptom.
 
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Heat shield is most likely. What kind of rattle is it? Any new noise is generally related to the last thing you changed. I'd check the two bolts that hold the muffler to the cat, and the clamp that holds the tailpipe to the muffler. I had a situation once on my old truck where a dealer "helped" me out and tightened a clamp for me. It was fine, until I loaded up my boat which compressed the suspension to a different point and then when I went over a bump, the bolt for the clamp was hitting a skid plate and making an AWFUL racket. I actually delayed a vacation because of it. Finally found it, loosened the clamp, rotated it and tightened it back up. That sound was never heard again!
 
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Ranger_b0b said:
Heat shield is most likely. What kind of rattle is it? Any new noise is generally related to the last thing you changed. I'd check the two bolts that hold the muffler to the cat, and the clamp that holds the tailpipe to the muffler. I had a situation once on my old truck where a dealer "helped" me out and tightened a clamp for me. It was fine, until I loaded up my boat which compressed the suspension to a different point and then when I went over a bump, the bolt for the clamp was hitting a skid plate and making an AWFUL racket. I actually delayed a vacation because of it. Finally found it, loosened the clamp, rotated it and tightened it back up. That sound was never heard again!
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The sound is like a tick. Faster the jeep moves, the quicker the tick. I am about to get back under and will double check these suggestions. Will update. And thank you for the response!
 
TenThumbs said:
The sound is like a tick. Faster the jeep moves, the quicker the tick. I am about to get back under and will double check these suggestions. Will update. And thank you for the response!
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Hmm...Does it happen all the time? Ticks that are speed sensitive...I'd start looking at my tires...you might have a stone in there! Its a quick check that doesn't cost anything...
 
Tires are clear of any debris. And there is no tick at low speed unless I give a fair amount of pedal. The clamp (first photo) is also tight and clear of hitting anything. The muffler is not centered exactly to the cat (2nd pic) but is nice and tight. Will try and get it lined up better. Should there be any play/wiggle in the exhaust? Mine is super tight with no movement whatsoever. The tick sounds more like metal hitting a thinner metal.

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Looking at your last photo, it makes me wonder if you don't have just the slightest exhaust leak going on, there. The alignment between old and new is such that the gasket area gives the appearance of having the potential to leak. Not knowing for certain what your "ticking" noise sounds like, all I'm doing is guessing. I'd look into it, though. The exhaust is the only thing you've changed, so it's a possibility.
 
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Squatch said:
Looking at your last photo, it makes e wonder if you don't have just the slightest exhaust leak going on, there. The alignment between old and new is such that the gasket area gives the appearance of having the potential to leak. Not knowing for certain what your "ticking" noise sounds like, all I'm doing is guessing. I'd look into it, though. The exhaust is the only thing you've changed, so it's a possibility.
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Thanks for the response. This will be the next thing I pull apart and attempt to get lined up better. The muffler was much higher on the hangers than the cat and so I had to gently jack the cat up before tightening the bolt down and lowering. Really hoping that this is the issue. It's hard to describe a sound to someone via text. I'll jump under there this evening and see what I can do. Texas heat is keeping me from doing much outside today. The shop fan feels like a hairdryer!
 
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Ranger_b0b said:
Just an FYI @Squatch, there is no gasket between the muffler and cat pipe. Its a tapered fit. Looking at the picture, I'd guess exhaust leak too.
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Yeah, I know there isn't a gasket, actually. I was just in a hurry to get out the door, and couldn't for the life of me remember the technical term for the bell/flare (obviously still can't remember it!). I just wanted to get the idea across that it could very well be an exhaust leak based on what I was seeing in the pic. My referencing the "gasket area" is actually a little embarrassing, in hindsight. Appreciate you having my back, though, and keeping me on the straight and narrow! :)
 
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Ok, so life got in the way and I had to put this on hold for a bit. I'm sad to say that the Jeep has been parked since this issue while I handled non-Jeep related issues. After pulling the exhaust and test driving, the tick is gone. I am convinced that it was putting torque on the engine and making in tilt towards the rear of the jeep (fan angled and higher) since I had to jack the Cat converter up to get in line with the exhaust.

I am waiting on a response from the manufacturer, and if I do not get a fix for their product lining up correctly, I will replace.

So...any recommendations on an exhaust that someone is happy with and is a true bolt on part?
 
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It's a complete waste of money to buy "bolt-on" exhaust systems for our TJs. The smart guys will tell you (myself included) that the best solution is to go to your local exhaust shop and have them build you an exhaust system. Most of us paid around $250 at most (that's what I paid), which is 50% cheaper on average than all the supposed "bolt-on" systems (which to be honest, often don't fit that well anyways). Any exhaust shop can do this in about 2 hours tops.

I'm glad I didn't waste the money on one of those exhaust systems you see online. They're all marked up and overpriced.
 
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I did not know about this forum prior to purchasing this for $289. Retailer offered a return for credit since I no longer use the same CC that I purchased this with. I guess I could always use the store credit for other fun things to add on, but would rather find a replacement exhaust and come out about even.

But I've learned to either research /and/or ask on this forum before spending anymore $.
 
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Well, I've figured out the clicking sound. The catalytic converter had to be raised to line up with the new muffler. This put pressure on the transmission, which changed the angle of the driveshaft. Once I removed the muffler and test drove her, the clicking is gone, but is replaced by a horrid clunk/thump sound and a bad shimmy. So, yay!, I've just created a whole new issue by installing a "bolt on" muffler. Looking like research, $$ and some wrench work are in my near future.

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Chris said:
It's a complete waste of money to buy "bolt-on" exhaust systems for our TJs. The smart guys will tell you (myself included) that the best solution is to go to your local exhaust shop and have them build you an exhaust system. Most of us paid around $250 at most (that's what I paid), which is 50% cheaper on average than all the supposed "bolt-on" systems (which to be honest, often don't fit that well anyways). Any exhaust shop can do this in about 2 hours tops.

I'm glad I didn't waste the money on one of those exhaust systems you see online. They're all marked up and overpriced.
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I dont understand how a complete system could cost only $250 when a full system, Crown or Magnaflow (up front with the three cats) plus the cat-back piece runs over a grand. You could save a couple bucks by getting a cheap front exhaust, say $700 all-in, but that $250 seems abnormally low.

I went to my local exhaust shop for tips, and they wanted $150 just to fabricate me two tips. I even called a known Audi exhaust shop, 42 draft designs, and they wanted over $100 for two tips.
 
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