What does tapping on a muffler indicate according to the technician's observations?

Tapping on a muffler is a diagnostic technique used to assess its condition. If the sound produced by tapping is dull or hollow, it may indicate internal corrosion or deterioration, which suggests that the muffler is likely rotting due to chemical damage. This typically occurs because mufflers are exposed to harsh conditions, including moisture and corrosive elements from exhaust gases.

In contrast, if a muffler were in fine condition, tapping on it would produce a solid, crisp sound, reflecting its structural integrity and good condition. A completely clogged muffler would likely not produce any sound or change in sound quality upon tapping, and instead, indicate a severe obstruction. Additionally, tapping alone would not conclusively reveal too much back pressure; this would typically require further diagnostic measures like pressure tests or performance evaluation under engine load. Therefore, the indication of rotting due to chemical damage is the most precise interpretation when tapping on the muffler yields a poor sound quality.