。
I heard a strange noise.
Literal
I [topic-は] abnormal noise [object-を] heard.
異常な (いじょう, 'abnormal, unusual') is a な-adjective. 物音 (ものおと, 'sound, noise') — a compound of 物 ('thing') + 音 ('sound'), referring to ambient or unidentified noises. A simple narrative statement.