Translation:While entering, I ran into a group of noisy people.
I’m sure this means fell into rather than ran into, fell into as in “I fell into bad company” fell into suggests that the participant joined in with the noisy group. Ran into doesn’t suggest that you joined in with them, merely that you bumped into them.
"While" suggests an action that lasts for some time; "running into" suggests something that happens quickly. The English would be more idiomatic if it matched those two durations: "On entering/ Upon entering/ At the entrance/ As I entered, I ran into." I totally agree with Sitesurf that "I fell upon" OR "I ran into" OR "I came upon" are perfectly correct, commonplace, idiomatic equivalents in English for the French "Je suis tombe sur" [some people] legitimate English equivalents for "
I keep seeing answers rejected for not using a preferred translation for "en in these sentences. To my knowledge, an equivalent could be either "in," "while," or "by" and would all be acceptable. They each can be used to mean slightly different things, but would still pass as equivalent in these contexts.