The Quran is Allah’s speech revealed in an authoritative voice, yet gentle style to be read and pondered over. We can regard it as a letter from our Lord, the Sustainer and the Loving Protector. Therefore, it can be read silently or loudly.
The recitation of the Quran is a form of remembrance of Allah, which can be done aloud or otherwise. In view of this, the Quran can be recited silently or moderately loud, as there is no difference in it. Sometimes it is preferred to be read silently, for example when there are other people in the room or the mosque. It is best not to disturb others. However, if people are keen to listen to you then it is good to read it aloud in melodious and beautiful style.