"It's noisy inside the train."
I think it would be fine. With は it's the inside of the train that you're talking about and saying that it's noisy or annoying. With に you could mean someone or something else inside the train is noisy/annoying, but really you're only expressing where it is and not what.
You should say 'wa' for は when this is placed after the subject word or phrase. 電車の中 works as the subject word in Japanese. It might look funny for Indo-European languages people.
That could also be meaningful. The difference is a bit subtle. Let's compare some particles (and hopefully I get it right, I'm not by any means a native speaker). I'd love for someone more fluent to review this.
電車にうるさい -- (In or on or at) the train, (someone or something) is noisy. WIthout の中, it's a bit less clear that we're talking about the inside of the train, but you know, probably. It's also not clear if the noise is actually coming from the train itself.
電車の中にうるさい -- Now we're talking about something going on inside the train for sure. Something unspecified inside the train is noisy.
電車でうるさい -- Using the train, (someone or something) is noisy. Well, I translated it as "using" here, but で sort of sets the context where some action is taking place. そこに投げる means to "throw something to there", while そこで投げる means "throw something while standing there". The で particle also has a much stronger sense that the noun it's marking is being used in some way to perform the action. Maybe here we're talking about a kid who is being noisy while riding the train. Maybe we're talking about a disgruntled conductor who is screeching the brakes as he goes by the minister of transport's house.
電車の中にはうるさい -- As for the inside of the train, it's noisy. Here we're definitely talking about the inside of the train in general. には sets the topic of discussion as well as telling us a location that something is targeting, we're talking about the place, and that something is making it noisy there.
電車にはうるさい -- As for at the train, it's noisy. More naturally: It's noisy where the train is. Again, we could be talking about the inside, I'm pretty sure we could be talking about standing at the platform when the train arrives. We're definitely discussing the location of the train, and not so much something else which happens to be there.
電車はうるさい -- As for the train, it's noisy. Or: The train is noisy. We're talking about the train itself. It's still possible that we're talking in general about what it's like to ride the train -- maybe it's people who are to blame. But the likelihood is that we're referring to the noise the train itself makes.
電車の中はうるさい -- As for the inside of the train, it's noisy.
電車ではうるさい -- As for using the train, it's noisy. The topic of discussion is the train, and it's the context by way of which things are taking place. Maybe we're contrasting what taking the train is like relative to other forms of transportation.
And as usual, we can add です to make it a little more polite/distant. Probably a good idea with this word, as it also gets used as an interjection to tell people to shut up.
To use 中には, you would have to reference something physical being inside. Descriptions are just 中は.
I would assume that this isn't describing the Japanese train/subway system because it's dead silent in those things lol
にぎやか can also mean noisy (positive connotation compared to うるさい, which has a more negative connotation). Reported.
It is an informal, rather rude/rough, masculine way of saying うるさい which means noisy but has the implication that you wish someone who is being noisy would stop being noisy.