What is expected from the sound of the muffler?

The correct answer focuses on the critical aspect of vehicle safety and public health. A muffler's primary function is to reduce the noise produced by the engine, ensuring that it operates at a volume that is not harmful to the ears. Excessively loud noises can be detrimental to hearing over time, both for the driver and for bystanders. Therefore, the muffler should maintain a sound level that is comfortable and does not pose a risk of auditory damage.

A loud muffler, while it may indicate a performance characteristic for some, can lead to nuisance and legal issues, especially in residential areas or noise-sensitive zones. Similarly, a barely audible muffler may not effectively mask harmful sounds from the engine, which can be detrimental to both safety and compliance with noise regulations. Pitch variation in the sound may also occur due to engine performance but does not directly address the primary concern of ear safety. Thus, the expectation that a muffler must not cause damage to the ears is essential for ensuring both public safety and adherence to legal noise standards.