The iconic "clickety-clack" sound of a train is caused by the wheels passing over rail joints. In traditional track construction, steel rails are laid in sections with small gaps between them to allow for thermal expansion—the metal expands in the summer heat and contracts in the winter. As each wheel set (bogie) hits these gaps, it creates the rhythmic percussive sound. However, this sound is becoming rarer on modern high-speed lines in 2026. Many railways now use Continuously Welded Rail (CWR), where the gaps are eliminated by welding the rails into miles-long single pieces. These tracks use heavy-duty "tensioning" systems to manage expansion without gaps, resulting in a much smoother, quieter "hum" rather than the traditional clack. You are most likely to hear the classic noise on older branch lines, freight tracks, or historical railway routes.