Thanks to electric power, the Eurostar is not noisy. However it is not either very silent. The speed and vibrations generate a constant underground noise that is not disturbing, but can be hypnotizing after a while. You can easily have a conversation with the person next to you without having to shout, as opposed to some areas in most aircrafts. In fact, it is quite easy to overhear conversations and sometimes people should be made aware that they are not alone!