Błędnie: He was pacing the room and thinking loud at the same time. Poprawnie: He was pacing the room and thinking aloud at the same time.
"Loud" oznacza 'głośny, hałaśliwie', 'głośno'. Odpowiednikiem 'na głos' jest "aloud" albo "out loud", np. The child cried out loud at the sight of the dog coming near.