Why do the metro's Azur trains have a high-pitched whistling noise?


For some metro users, a ride on the new state-of-the-art Azur trains might feel like they're bit players in some kind of horror movie.

The STM says at least 95 people have called or written to complain about a sharp, high-pitched whistling noise coming from the trains, which began cropping up last winter.

Unlike its predecessors, the Azur trains fall silent when they're stopped inside a station to take on passengers. But as they power up to leave, the whistling would begin, and continue for the entire ride to the next station.

Users have also noticed the noise would be more pronounced in the back of the train than the front.

So where is it coming from?

Train modification to blame

"The whistling we can hear inside the Azur trains is caused by the release of air that comes from inside," says STM spokesperson Isabelle Alice Tremblay. "Because the Azur trains are Boa-type trains, that is, completely open trains allowing free movement from one car to another, there's a significant movement of the air in the cars."

She also notes the problem was exacerbated by a modification to the trains made last winter by their maker, the Bombardier/Alstom consortium.

The company installed kick-plates underneath the trains' doors, to prevent the accumulation of salt, gravel, and other winter debris inside the mechanism of the doors, which prevented them from closing properly and, in turn, caused service delays.

Tremblay says while they've managed to eliminate the service delays with the new piece of equipment, more air trapped inside the train gets released, causing the whistling noise. She also says it's barely noticeable when the trains are packed, and much more noticeable during off-peak hours.

The transit agency says Bombardier/Alstom are aware of the problem, and are currently working to fix it.