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Discussion Starter #1 (Edited)
To start out I have a 1999 miata with a racing beat axle back and a resonator delete via a local exhaust shop. This seems to have started when I deleted the resonator in my '99. After this, when the exhaust is cold (coolant/oil temp don't seem to matter very much, if the car has had 15 minutes sitting it will make the noise.) it has a rasp/rattle/**** honda noise starting from around 3k revs to 6k. My best guess so far is a piece of weld floating around in the muffler or the muffler falling apart. For shits and gigs one day I took off the muffler and didn't notice the noise and when I put it back on it didn't make the noise for the 1st time I drove it afterwards. :dunno: I'm thinking this may be something to do with the muffler but I'm not sure; do miatas usually sound rice after a resonator delete or is it something in my muffler causing this sound?
 

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Motorboat Captain
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A resonator helps reduce resonance. Being such as that is and in wholly picture of it all, if you take off the resonator, and your exhaust is going to resonate.
 

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enormous gay swords.
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Don't remove the cat...it'll only get worse.

Put a resonator back in and throw a header on. That will increase the volume while getting a resonator back in the system. Resonators don't do much for noise reduction, they're all about smoothing the exhaust tone.
 

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Discussion Starter #9
My only question now is why does the noise go away while the muffler was taken off? This is what confuses me. And since the resonator is long gone, would you recommend an aftermarket mid pipe or just weld a new resonator in place of the old one?
 

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First thoughts would be that you just couldnt notice the noise with the added sound levels of running no muffler. Second thoughts would be that adding the muffler back in without the resonator altered the resonance frequency of the entire system to cause the noise youre hearing. I know of a few people who have had drone issues with a resonated midpipe vs a clear[er] tone without. My car has a weird **** box noise from around 4500-5500 as well, but I just kinda deal with it. Make sure you dont have an exhaust leak of any sort either tho. I could imagine a leak of any sort causing some strange pinging regardless of how your exhaust is set up.
 

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Discussion Starter #11
Here is a sound clip from a cold start. the sound changes a lot while driving but idk how to capture it(lost my gopro suction mount).
 

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From the first post, it sounds like something is loose within the muffler. Try tapping the exhaust from the cat to the rear muffler to see if you can replicate the rattle. If it is just a rasp, then it's probably like everyone else is saying-- need more mufflers/resonators and a good cat.
 

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Discussion Starter #15
Looked very thoroughly for exhaust leaks and there is none to be found. I also did some tapping on the exhuast from the cat back and on heat shields. When I got to the muffler I did hear something almost as if there was a bunch of super tiny pebbles moving around in there. I also saw some markings on the bottom as if the muffler was scrapped against the ground. I'm definitely leaning toward the muffler now. if I were to replace it I would be looking for something with a little more noise than the racing beat, what kind of brands should I look at for a muffler?
 

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Motorboat Captain
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Buddy Club Spec 2 and call it a day.
 
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