Originally Posted by CGII
Are you talking about noise as experienced from within the car or from outside? Because from outside an Amtrak train sounds about as loud as any subway.
The new R160 cars that are gradually replacing older cars have improved insulation and seals and they are significantly quieter than the older cars.
Also I have to say what's already been mentioned; Chicago's trains are effin' loud.
I guess that supports my hypothesis.
The loudest noises come from the train wheels hitting the gaps between consecutive tracts - since it happens a lot over the length of the train, and because it's happens in an enclosed tunnel underground, this noise multiplies and intensifies. My guess is that the air-conditioning in Amtrak and commuter trains are also significantly quieter than the AC systems in older subway cars.
And last, but not least, is the amount of sound insulation and window/door seals used in the different train cars. Older subway cars don't use a lot, while Amtrak/commuter trains have to use a lot.