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Not all the time, just every once in a while, my exhaust when I crank up my car will be loud as if it has no exhaust under the car. After I get going down the street it will become quite again. I hope one of you can give me a reason why it does this.

Thank you for your time,
Daniel
 

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cant help from behind the laptop... leak can happen from the exhaust manifold or any flanges.

hopefully, you got a buddy to help you locate the noise

some local shops offer free inspections of the exhaust as well

a few youtube vids of how to cram a shop vac up the tailpipe to pressurize the pipes... then use soapy water spray bottle and check where possible air leaks from an exhaust flange to flex pipe to oxygen sensor connection...

or just a plain visual might help you find it
 

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Most Mazda will be loader when first started that is normal until the H02 get heated and send the signal to the ECU which changes perimeters of fuel mixture and timing, etc., during the engine warm up cycle. Unless you take a good video it would be hard for anyone to "guess" your specific noise.

BTW it really help to always state your year model, engine and transmission when asking for help!
 

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2022 Mazda 3 Premium 2.5 NA
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Not sure about the year, but my 22 is loud on a cold start, it’s to heat up the cat. From what I read has to do with the 4-2-1 header cooling the exhaust gases before the cat.
 

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well not exactly ^^.... the HO2 sensors (freqently miss called O2 sensors) control the AFR during start mode not really relating to the CAT. After they are warmed/Heated ( H=heated in the HO2 which means Heated Oxygen Sensor) go to closed- loop operation which they constantly send information to the ECU which in turn uses to regulate the AFRs.


The Exhaust system mentioned developed by MAZDA simplified explanation was more to utilize back pressure control scavenging attempting to maintain a greater exhaust velocity by keeping the exhausts temperature's maintained longer after they left the exhaust port of the head. This was to help increase the power output at lower engine speeds and also support lowering the exhaust emissions.
 
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