As some of the guests already mentioned, the street is very noisy, especially in the night. This is because right under the apartment on the corner is something like drug dealers hangout group from 3 to 5-6 people, that are very loud in the evening and night, shouting at everyone if they need "something". I think they are under influence themselves as they were really SCREAMING and crying every night...
Because of that it's impossible to open the windows in the night and it was really hot and no air in the very little apartment (there is no vent or AC).
Those are the negative things that affected my stay.
Other than that the apartment is really lovely and even though it is tiny, there is all you need, the location is great, and Lisbon is magnificent!!