He was just in time to hear an unusual sound.

She chuckled, an unusual sound in the past several days.

No unusual sounds were heard and nothing out of the ordinary occurred.

Though she'd seen no movement nor heard any unusual sound, something was out there watching them.

One of the guards, hearing the unusual sound, turned around.

It has an unusual sound, but then so does your voice.

This scale has quite an unusual sound and takes a little getting used to.

At the slightest unusual sound, it would be gone like a flash.

This was followed by a more unusual sound: the bolt being drawn across.

"Did you hear any unusual sounds that evening between eight and nine o'clock?"