Investment Near Noisy Train

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Interested to get advice on what range of discount people have seen on properties that are adjacent to loud public transportation. I'm looking at a brick 3-Flat in Chicago that is immediately next to the elevated train line. Since this would be buy-and-hold, I'm not overly concerned with resale value at this time, but curious on what this might mean for rent and how I should factor that into an offer. The seller has provided the rent roll but as typical, they claim these are below market rents. Thanks for the help.