Why is the Mazda engine start-up noise so loud?

[Molly]

Mazda's loud cold start noise is due to the arrangement of the exhaust manifold, which positions the three-way catalytic converter too far back. The three-way catalytic converter must reach a certain temperature to effectively filter exhaust gases. Therefore, to rapidly heat up the three-way catalytic converter, the exhaust valve closure is deliberately delayed during cold starts, causing the air-fuel mixture to enter the exhaust manifold and undergo detonation, resulting in the loud cold start noise. More information about Mazda is as follows: Overview: Mazda, officially known as Mazda Motor Corporation, is a Japanese multinational automaker listed on the Tokyo Stock Exchange (TYO). Its business scope includes passenger cars, automobile manufacturing, and sales. Models: Mazda's global passenger car lineup includes: SUV series CX-3, CX-30, CX-4, CX-5, CX-8, CX-9, MX-30; Sedan series Mazda2, Mazda3, Mazda6 (known as "Atenza" by FAW Car); Sports car MX-5.