Why Does a Cold Exhaust Drone?

[ShamrockShooter]

I've noticed my borla exhaust sounds pretty good once it's warm, but on cold starts and the first few miles it seems much louder and has an annoying droning resonance at certain rpms that goes mostly away when warm.

 

So why does an exhaust sound louder or drone when it's cold and quiet down when warm?

 

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[Justin101714]

Well, metal contracts and expands depending on temperature, so that could be enough to cause certain exhaust frequencies to carry more into the cabin than when it's cold rather than when it's warm.

 

 

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[DanMan_S]

I've noticed my borla exhaust sounds pretty good once it's warm, but on cold starts and the first few miles it seems much louder and has an annoying droning resonance at certain rpms that goes mostly away when warm.

 

So why does an exhaust sound louder or drone when it's cold and quiet down when warm?

 

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The engines run rich during a cold start; the ECU is dumping in extra fuel so it changes the behavior of the combustion and the resulting exhaust note.

[SkiDooNick700]

What he said ^. You should notice it's a lot more aggressive sounding too at idle when engine has been cold soaked.

['17 Sierra]

Spark timing is the main reason.