Is it necessary to raise one's voice when saying the Basmala before eating, or is it permissible to say it silently?

It is not obligatory to say "Bismillah" (In the name of Allah) aloud before eating; rather, it suffices to say it silently by moving the tongue, in compliance with the command of the Prophet, peace and blessings be upon him. However, it is preferable to say it aloud to remind people and to teach the ignorant. Ibn Hajar al-Haytami justified the recommendation of saying "Bismillah" aloud to alert those eating to it and to the commencement of eating, while saying "Alhamdulillah" (Praise be to Allah) silently after finishing is out of fear that some may not have finished eating yet. As for drinking, one has the choice between saying it aloud or silently, unless one is a scholar whose example is followed, in which case it is sunnah for him to say it aloud to teach the Sunnah.