Matthew Poole and continuators on John 12:29

29 The people therefore that stood by, and heard it, said that it thundred : Others said, An ang[illegible: 1 letter]l spake to him .

Nor it may be were they mistaken, saving onely in this, that they thought it was nothing else but thunder, (being possibly at such a distance, as they could not distinctly hear the voice) for it was Gods way, when he spake unto his people by a Voice, to have that voice for the greater declaration of the Divine Majesty, attended with Thundrings and Lightnings: thus it was at the giving of the Law upon Mount Sinai; thus we read in Iohns Visions, Rev. 4.5. and 8.5. Of Lightnings, and Thundrings, and Voices, which proceeded from Gods Throne.

It was the general opinion of the Iews, that God always, when by Voice he revealed his mind to his people, made use of an Angel to do it by, hence (probably) as those who were at such a distance, as they heard no Voice, thought it was nothing but Thunder; so those who were so nigh, as beside the Thunder to hear a Voice, said, It was an Angel that spake with him.