It's from the power cutters which protect the electric system from an overcharge during the acceleration phase. It's a very unique and awesome song. I'm glad they immortalised it this way so that when the dreaded time of the MR-73 replacement comes, it will forever remain as a reminder of the Montreal Metro "heroic times".
I used to work in the Sunlife building and took the orange line every day. Bonaventure was my stop. Haven't been there since 2013. That was an exciting time for me and seeing the station in your video brought back a lot of feelings from that period. I always felt that the Metro was a sort of portal into the world and never took for granted how amazing it was to zip around town in underground tunnels. I've also never took for granted how every station is unique and beautiful. Sometimes I want to work downtown again just to have a reason to leave the car home and take the Metro.
Montreal has the best metro, perfect sound of door closing, great sound of acceleration, I hope they gonna put the same amount of m73 and azul in each color lines instead of removing m73 to be replaced by full azul
I wish the mic on your camera was better to capture the three tones the train makes on acceleration with more fidelity; at least until the sound of the train moving becomes too loud. I'd love to make the tones a ringtone or sound affect of some sort.