On most railways, the gaps are opposite each other and if the carriages are about the same length as the rails, an even clickety clack sound is generated.
Several distinct sounds are created by various parts of the train, such as engines, traction motors, brakes, and the wheels rolling on the rails.
The "Howling sound" is caused by lateral sticking and slipping of the wheels across top of the railroad track.
The MBTA Green Line, for example, suffers from severe rail squeal on the sharp curves within the central subway.
Flange stick graphite lubricators have been installed on trains to attempt to mitigate the rail squeal issue.