I think it’ll mainly be when you go. The less people, the better! I take the train every day for work. Generally everyone likes to stay pretty quiet and on their phone, but it can be squished, making getting in and out potentially bumpy for you and the carrier. That’s also just the train in my area though. Other places train habits may be different!

I really recommend a pee pad on the carrier that covers it entirely. Last thing you want is pee leaking onto you or those around you!

How long is the ride? If it’s less than an hour, I don’t see an issue with her overcoming it, at the worst being she may be shaken up until you set her somewhere and give her food. Maybe put her in a carrier, place it in from a TV, and turn the sound on louder than usual. See her reactions.

If she seems bug eyed and frozen, then the train isn’t a good idea, but she may just erect her ears and sit instead. That’s a more tolerated reaction to noise.

I don’t have experience with that line, but I can’t imagine the trains can get to a crazy volume. You should check if there are quiet ride cars on the train! Some train services make the first car quiet ride ones during rush hour/busier times.

I also live in Chicago, and regularly take the red line, and it does get pretty loud, but I think it might be worth a try. I want to know how it goes because I also need to do some bunny traveling via train, also have you ever taken the Metra with your rabbits?