。
His voice is drowned out by the evil spirit's sudden roar.
Literal
His voice [topic-は] evil-spirit [possessive-の] sudden roar [by-に] is-drowned-out.
かき消される is the passive of かき消す — literally 'scratch-erase' but meaning 'to drown out' or 'swallow up' a sound. The に marks the agent in this passive construction. 悪霊の突然の咆哮 stacks two の-linked modifiers: 'evil spirit's sudden roar.' 咆哮 (roar/howl) is a vivid, literary vocabulary choice over the simpler 叫び.