And the last time I was back the skytrain sounded way lounder. Not sure if it is my memory or wear-and-tear.
this is a weird flex but i may never get another chance to use it. i briefly worked at the london underground a very long time ago as a student and actually reviewed this as part of an evaluation on whether to refurbish or replace old rail cars. they did a bunch of testing of old and new rail cars including a 1960s vip train that barely got used.
short answer is you probably are not imagining it. they may be delaying maintenance on rail wheels and tracks, which is the main cause of external noise and a lot of internal noise, but general rail car wear and flex is also likely contributing to internal noise. the flex problem is likely worse on corners. you cannot fix it with refurbishment and you might make it worse if you try.
also, it turned out the low mileage 1960s rail car was much quieter than their brand new 1980s trains. so they solved that by taking the vip train out of the graph in the study.
their overall solution was to replace track and rail wheels more frequently and run the old trains into the ground. a sidebar to this was that it being the 1980s in the uk the london underground hired tons of unemployed people at minimum wage to do the rail work (overnight). anyone refusing the job was cut off benefits. i worked at their training centre briefly. the state of the people shuffling into the introductory training sessions on a monday morning was something to behold.
finally, there were also people who clean subway tunnels at night. they were called fluffers and were all women and among other things they literally dusted the tracks between stations to reduce wear. some years later i learned this term is also used in a different industry.
the more you know.
