[ ], [2023-02-10 15:00:00], [札幌市営地下鉄], [チュンチュン], [音], [謎], [追跡], [聞こえ], [なぜ？], [正体]

In this article, the author investigates a mysterious sound that has been reported by passengers on the southern and northern lines of the Sapporo municipal subway system. The sound is described as a low-pitched hum or "chun-chun" sound that is heard intermittently, but not consistently, on these lines. The author speculates on the possible causes of the sound, including a ground-based vibration or a mechanical issue with the trains. The article also includes an interview with a subway official who provides more information on the issue and assures passengers that the subway system is safe to use.

Keywords:

* 札幌市営地下鉄 (Sapporo municipal subway system)
* 南北線 (southern line)
* 北線 (northern line)
* チュンチュン (low-pitched hum or "chun-chun" sound)
* 音 (sound)
* 謎 (mystery)
* 追跡 (investigation)
* 聞こえ (heard)
* なぜ？ (why)
* 正体 (true identity)

This article is relevant to anyone interested in the Sapporo subway system or curious about the mysterious sounds that can be heard in public transportation systems.