“Om, the Hindus’ Sacred Syllable, said or sung before and after prayers, ends with a fourth sound beyond the range of human hearing. This sound is called the “sound of silence.” It is also called “the sound of the universe.” Hindus, in the repetition of the Sacred Syllable, try to go beyond thought, to reach the stillness and silence that constitutes God.” — from Chris Hedges, The World As It Is, p. 35
This is beautiful. One can imagine the Tetragrammaton (YHWH) and ALLH (also four letters in Arabic) also has a silent syllable. More important, I read in the Description of the Prophet’s Prayer by Sheikh Albani (رحمت الله عليه), that one should pause after reciting every verse in the Qur’an in the tradition of the Prophet (صلى الله عليه وسلم) — indeed, the Prophet’s (صلى الله عليه وسلم) recitation of his prayers included the silent syllables, and we should not ignore those. Introverts often have feelings deeper than words, we can say these are spoken in silent syllables.