The short version
Nguyen Trai is a long south western corridor of universities, apartment towers, older lanes and the Line 2A viaduct. It is highly convenient for local services and transport, but street calm is not its selling point. Choose the exact side street and the direction of your daily travel.
The metro is the corridor’s practical advantage. Hanoi Metro’s Line 2A runs from Cat Linh towards Yen Nghia, so the route is useful for people whose work follows it. The viaduct and arterial traffic also shape the sound, crossings and view. A rear facing flat is worth seeking; a balcony over the main road needs an honest inspection.
I would live on a quieter side street near the station I needed. Nguyen Trai is a connected working corridor, not a place to hide from traffic.