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Yes, there are many components to train noise.

I used to live by rails with a small incline, and the diesel locomotives made a loud low noise accelerating uphill from a station, while downhill the trains moved far faster and the engines were quite insignificant compared to noises due to speed: mainly the wheel noise and going over the expansion joints.

We lived fifty yards from a railroad embankment, just where it bridged a street. It was very loud.

you see, why? ;-)

huh. rubber on asphalt is very loud on high speeds, could steel on steel really be quieter? (for downvoters: this is a real question, I'm not trying to suggest it can't be)

Yes, because rubber and asphalt do not really have a smooth surface unlike polished steel. So all the little bumbs give your car grip, but also cause friction, which is noise.

One of the reasons, why trains are better suited in theory for long distance transport, than trucks. Little friction, so more energy efficient.

Friction produces heat, not sound...

Both. What are the rapidly heated molecules going to do? Create turbulence in the air. That is sound.