You're close.
"I heard that in order to prevent people from running on to trains at the JR Tokyo Station's Shinkansen platform they've changed the bells that signal departure to melodies. When you hear a harsh bell, certainly you'll get frantic and run onto the train."
I went with trying to keep the English as close to the Japanese as possible in the sense of the meanings of words more so than the mood, so it's not the best translation. A few points:
〜したんだって is used to quote something indirectly.
激しいベルを聞くと is "when (people) hear a harsh (violent) bell," and what follows is a natural sort of reaction to it (i.e., you get flustered and end up running onto the train). That's the sort of defining characteristic of と versus なら, たら, and ば.
走って乗ろうとしちゃう contains a lot. 走って乗る is "board running," that is the 走って can be looked at like an adverb here: it's describing how you're boarding the train. しようとする means to try to do something, so 乗ろうとする means try to board (the train). -てしまう means "do something regrattably/irreversibly," and here it has a sense that running onto the train would end up with undesireable results. -てしまう often gets contracted to -ちゃう in casual speech.
Good info to have!
