The trains in Japan are kewl - you know how you can always hear the "clack-clack, clack-clack" of the wheels going over the rail joints? Well, some segments of rail there are continuous-cast on the spot, and so they're seamless. I have no idea how they temperature compensate them. But anyway, it's kinda weird and kewl when the "clack-clack" stops and the car goes essentially silent except for the rush of the air.
I also don't know if the US trains are doing this.
Cheers! Rich