In the case that I might offend you somehow unintentionally, please forgive me if I say something blatantly obvious. Please keep in mind that I am in no way, shape, or form fluent in any other language than English, and have little experience speaking other languages. I really appreciate how well you speak.
I might describe the noises a train makes as thunderous and rhythmic, but it depends on where you are. Are you at a train station? Is the train above or below ground? (If you have been to some place like New York and have ridden the subway (sometimes referred to as a train) you will know that there is a huge difference between the sounds of the two. A subway train sounds squeakier.
Anyways, here is how it might look in a sentence if you are talking about an above-ground train:
The train made a low, thunderous noise if you were a mile away, but up close you could hear the rhythm of each car as it passed over the tracks and the squeakiness of its many rivets.
Depending on how crowded and where the train is, you may be able to hear individual conversations here and there. If there are a lot of people, it sounds more like static on a radio, since you can't make anything out. I know English is your second language, and I certainly cannot speak your native language as well as you speak English, (whatever language it is...) but I am not quite sure what you mean by exchange, so I will just guess... Here is something that I might write about what the other passengers say to each other. Its not great, but hopefully you can get something
out of it:
The other passengers on the train chatted incessantly. Sometimes one could make out a word here or there, but often one person's words would be drowned out by another's, and most of the time one can't make out much at all of what another person might be saying. The result was an ongoing murmur, resembling very much the static one gets on the radio when out of range. More than once one could pass by some people that spoke in a foreign tongue. If one listens closely, one might be able to make out a pattern, but that rarely happens.
I see now that you are describing passengers getting on and off. What I would say is come and go, enter and exit, or even switch places with each other as one gets on board and another leaves, etc.
Okay, that last one is rather easy. You could use the words sparse, meager, or sporadic if there are just a few people there. Of course, these words are better if there are a less than average number of people there. If you want to say that there are an average number of people at the station, you could say reasonable amount, half full, etc.
There really isn't an English word for a middle quantity, unless I am forgetting something.
Okay, so something that might be helpful is that you could use some train noises in the background and draw some people, but I understand from others that backgrounds are difficult to do.
Here is what I would do:
Autumn is here.
Perhaps it is not a season that everyone looks forward to, but it is a special season for some.
Like (insert person's name here).
The sound of the train wheels on the tracks can be heard from afar.
The green light turns to red.
The few people here get up from their wooden benches as the the squeaking of the train's rusty wheels reaches a crescendo.
There it is, sharp at eight o'clock, the train slows down steadily at its station.
A few people exchange places, some hopping out onto the platform, some stepping onto the train.
Thankfully, it wasn't crowded.
I know that was really long-winded, but I hoped that I have helped you in some way, shape, or form.
A teenager's favorite phrase:No sé y no me importa.
Translation: I don't know and I don't care